module.c

/*
 * Copyright (c) 2016, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "server.h"
#include "cluster.h"
#include <dlfcn.h>

#define REDISMODULE_CORE 1
#include "redismodule.h"

/* --------------------------------------------------------------------------
 * Private data structures used by the modules system. Those are data
 * structures that are never exposed to Redis Modules, if not as void
 * pointers that have an API the module can call with them)
 * -------------------------------------------------------------------------- */

/* This structure represents a module inside the system. */
struct RedisModule {
    void *handle;   /* Module dlopen() handle. */
    char *name;     /* Module name. */
    int ver;        /* Module version. We use just progressive integers. */
    int apiver;     /* Module API version as requested during initialization.*/
    list *types;    /* Module data types. */
};
typedef struct RedisModule RedisModule;

static dict *modules; /* Hash table of modules. SDS -> RedisModule ptr.*/

/* Entries in the context->amqueue array, representing objects to free
 * when the callback returns. */
struct AutoMemEntry {
    void *ptr;
    int type;
};

/* AutMemEntry type field values. */
#define REDISMODULE_AM_KEY 0
#define REDISMODULE_AM_STRING 1
#define REDISMODULE_AM_REPLY 2
#define REDISMODULE_AM_FREED 3 /* Explicitly freed by user already. */

/* The pool allocator block. Redis Modules can allocate memory via this special
 * allocator that will automatically release it all once the callback returns.
 * This means that it can only be used for ephemeral allocations. However
 * there are two advantages for modules to use this API:
 *
 * 1) The memory is automatically released when the callback returns.
 * 2) This allocator is faster for many small allocations since whole blocks
 *    are allocated, and small pieces returned to the caller just advancing
 *    the index of the allocation.
 *
 * Allocations are always rounded to the size of the void pointer in order
 * to always return aligned memory chunks. */

#define REDISMODULE_POOL_ALLOC_MIN_SIZE (1024*8)
#define REDISMODULE_POOL_ALLOC_ALIGN (sizeof(void*))

typedef struct RedisModulePoolAllocBlock {
    uint32_t size;
    uint32_t used;
    struct RedisModulePoolAllocBlock *next;
    char memory[];
} RedisModulePoolAllocBlock;

/* This structure represents the context in which Redis modules operate.
 * Most APIs module can access, get a pointer to the context, so that the API
 * implementation can hold state across calls, or remember what to free after
 * the call and so forth.
 *
 * Note that not all the context structure is always filled with actual values
 * but only the fields needed in a given context. */
struct RedisModuleCtx {
    void *getapifuncptr;            /* NOTE: Must be the first field. */
    struct RedisModule *module;     /* Module reference. */
    client *client;                 /* Client calling a command. */
    struct AutoMemEntry *amqueue;   /* Auto memory queue of objects to free. */
    int amqueue_len;                /* Number of slots in amqueue. */
    int amqueue_used;               /* Number of used slots in amqueue. */
    int flags;                      /* REDISMODULE_CTX_... flags. */
    void **postponed_arrays;        /* To set with RM_ReplySetArrayLength(). */
    int postponed_arrays_count;     /* Number of entries in postponed_arrays. */
    void *blocked_privdata;         /* Privdata set when unblocking a clinet. */

    /* Used if there is the REDISMODULE_CTX_KEYS_POS_REQUEST flag set. */
    int *keys_pos;
    int keys_count;

    struct RedisModulePoolAllocBlock *pa_head;
};
typedef struct RedisModuleCtx RedisModuleCtx;

#define REDISMODULE_CTX_INIT {(void*)(unsigned long)&RM_GetApi, NULL, NULL, NULL, 0, 0, 0, NULL, 0, NULL, NULL, 0, NULL}
#define REDISMODULE_CTX_MULTI_EMITTED (1<<0)
#define REDISMODULE_CTX_AUTO_MEMORY (1<<1)
#define REDISMODULE_CTX_KEYS_POS_REQUEST (1<<2)
#define REDISMODULE_CTX_BLOCKED_REPLY (1<<3)
#define REDISMODULE_CTX_BLOCKED_TIMEOUT (1<<4)

/* This represents a Redis key opened with RM_OpenKey(). */
struct RedisModuleKey {
    RedisModuleCtx *ctx;
    redisDb *db;
    robj *key;      /* Key name object. */
    robj *value;    /* Value object, or NULL if the key was not found. */
    void *iter;     /* Iterator. */
    int mode;       /* Opening mode. */

    /* Zset iterator. */
    uint32_t ztype;         /* REDISMODULE_ZSET_RANGE_* */
    zrangespec zrs;         /* Score range. */
    zlexrangespec zlrs;     /* Lex range. */
    uint32_t zstart;        /* Start pos for positional ranges. */
    uint32_t zend;          /* End pos for positional ranges. */
    void *zcurrent;         /* Zset iterator current node. */
    int zer;                /* Zset iterator end reached flag
                               (true if end was reached). */
};
typedef struct RedisModuleKey RedisModuleKey;

/* RedisModuleKey 'ztype' values. */
#define REDISMODULE_ZSET_RANGE_NONE 0       /* This must always be 0. */
#define REDISMODULE_ZSET_RANGE_LEX 1
#define REDISMODULE_ZSET_RANGE_SCORE 2
#define REDISMODULE_ZSET_RANGE_POS 3

/* Function pointer type of a function representing a command inside
 * a Redis module. */
typedef int (*RedisModuleCmdFunc) (RedisModuleCtx *ctx, void **argv, int argc);

/* This struct holds the information about a command registered by a module.*/
struct RedisModuleCommandProxy {
    struct RedisModule *module;
    RedisModuleCmdFunc func;
    struct redisCommand *rediscmd;
};
typedef struct RedisModuleCommandProxy RedisModuleCommandProxy;

#define REDISMODULE_REPLYFLAG_NONE 0
#define REDISMODULE_REPLYFLAG_TOPARSE (1<<0) /* Protocol must be parsed. */
#define REDISMODULE_REPLYFLAG_NESTED (1<<1)  /* Nested reply object. No proto
                                                or struct free. */

/* Reply of RM_Call() function. The function is filled in a lazy
 * way depending on the function called on the reply structure. By default
 * only the type, proto and protolen are filled. */
typedef struct RedisModuleCallReply {
    RedisModuleCtx *ctx;
    int type;       /* REDISMODULE_REPLY_... */
    int flags;      /* REDISMODULE_REPLYFLAG_...  */
    size_t len;     /* Len of strings or num of elements of arrays. */
    char *proto;    /* Raw reply protocol. An SDS string at top-level object. */
    size_t protolen;/* Length of protocol. */
    union {
        const char *str; /* String pointer for string and error replies. This
                            does not need to be freed, always points inside
                            a reply->proto buffer of the reply object or, in
                            case of array elements, of parent reply objects. */
        long long ll;    /* Reply value for integer reply. */
        struct RedisModuleCallReply *array; /* Array of sub-reply elements. */
    } val;
} RedisModuleCallReply;

/* Structure representing a blocked client. We get a pointer to such
 * an object when blocking from modules. */
typedef struct RedisModuleBlockedClient {
    client *client;  /* Pointer to the blocked client. or NULL if the client
                        was destroyed during the life of this object. */
    RedisModule *module;    /* Module blocking the client. */
    RedisModuleCmdFunc reply_callback; /* Reply callback on normal completion.*/
    RedisModuleCmdFunc timeout_callback; /* Reply callback on timeout. */
    void (*free_privdata)(void *);       /* privdata cleanup callback. */
    void *privdata;     /* Module private data that may be used by the reply
                           or timeout callback. It is set via the
                           RedisModule_UnblockClient() API. */
} RedisModuleBlockedClient;

static pthread_mutex_t moduleUnblockedClientsMutex = PTHREAD_MUTEX_INITIALIZER;
static list *moduleUnblockedClients;

/* --------------------------------------------------------------------------
 * Prototypes
 * -------------------------------------------------------------------------- */

void RM_FreeCallReply(RedisModuleCallReply *reply);
void RM_CloseKey(RedisModuleKey *key);
void autoMemoryCollect(RedisModuleCtx *ctx);
robj **moduleCreateArgvFromUserFormat(const char *cmdname, const char *fmt, int *argcp, int *flags, va_list ap);
void moduleReplicateMultiIfNeeded(RedisModuleCtx *ctx);
void RM_ZsetRangeStop(RedisModuleKey *kp);
static void zsetKeyReset(RedisModuleKey *key);

/* --------------------------------------------------------------------------
 * Heap allocation raw functions
 * -------------------------------------------------------------------------- */

/* Use like malloc(). Memory allocated with this function is reported in
 * Redis INFO memory, used for keys eviction according to maxmemory settings
 * and in general is taken into account as memory allocated by Redis.
 * You should avoid using malloc(). */
void *RM_Alloc(size_t bytes) {
    return zmalloc(bytes);
}

/* Use like calloc(). Memory allocated with this function is reported in
 * Redis INFO memory, used for keys eviction according to maxmemory settings
 * and in general is taken into account as memory allocated by Redis.
 * You should avoid using calloc() directly. */
void *RM_Calloc(size_t nmemb, size_t size) {
    return zcalloc(nmemb*size);
}

/* Use like realloc() for memory obtained with RedisModule_Alloc(). */
void* RM_Realloc(void *ptr, size_t bytes) {
    return zrealloc(ptr,bytes);
}

/* Use like free() for memory obtained by RedisModule_Alloc() and
 * RedisModule_Realloc(). However you should never try to free with
 * RedisModule_Free() memory allocated with malloc() inside your module. */
void RM_Free(void *ptr) {
    zfree(ptr);
}

/* Like strdup() but returns memory allocated with RedisModule_Alloc(). */
char *RM_Strdup(const char *str) {
    return zstrdup(str);
}

/* --------------------------------------------------------------------------
 * Pool allocator
 * -------------------------------------------------------------------------- */

/* Release the chain of blocks used for pool allocations. */
void poolAllocRelease(RedisModuleCtx *ctx) {
    RedisModulePoolAllocBlock *head = ctx->pa_head, *next;

    while(head != NULL) {
        next = head->next;
        zfree(head);
        head = next;
    }
    ctx->pa_head = NULL;
}

/* Return heap allocated memory that will be freed automatically when the
 * module callback function returns. Mostly suitable for small allocations
 * that are short living and must be released when the callback returns
 * anyway. The returned memory is aligned to the architecture word size
 * if at least word size bytes are requested, otherwise it is just
 * aligned to the next power of two, so for example a 3 bytes request is
 * 4 bytes aligned while a 2 bytes request is 2 bytes aligned.
 *
 * There is no realloc style function since when this is needed to use the
 * pool allocator is not a good idea.
 *
 * The function returns NULL if `bytes` is 0. */
void *RM_PoolAlloc(RedisModuleCtx *ctx, size_t bytes) {
    if (bytes == 0) return NULL;
    RedisModulePoolAllocBlock *b = ctx->pa_head;
    size_t left = b ? b->size - b->used : 0;

    /* Fix alignment. */
    if (left >= bytes) {
        size_t alignment = REDISMODULE_POOL_ALLOC_ALIGN;
        while (bytes < alignment && alignment/2 >= bytes) alignment /= 2;
        if (b->used % alignment)
            b->used += alignment - (b->used % alignment);
        left = (b->used > b->size) ? 0 : b->size - b->used;
    }

    /* Create a new block if needed. */
    if (left < bytes) {
        size_t blocksize = REDISMODULE_POOL_ALLOC_MIN_SIZE;
        if (blocksize < bytes) blocksize = bytes;
        b = zmalloc(sizeof(*b) + blocksize);
        b->size = blocksize;
        b->used = 0;
        b->next = ctx->pa_head;
        ctx->pa_head = b;
    }

    char *retval = b->memory + b->used;
    b->used += bytes;
    return retval;
}

/* --------------------------------------------------------------------------
 * Helpers for modules API implementation
 * -------------------------------------------------------------------------- */

/* Create an empty key of the specified type. 'kp' must point to a key object
 * opened for writing where the .value member is set to NULL because the
 * key was found to be non existing.
 *
 * On success REDISMODULE_OK is returned and the key is populated with
 * the value of the specified type. The function fails and returns
 * REDISMODULE_ERR if:
 *
 * 1) The key is not open for writing.
 * 2) The key is not empty.
 * 3) The specified type is unknown.
 */
int moduleCreateEmptyKey(RedisModuleKey *key, int type) {
    robj *obj;

    /* The key must be open for writing and non existing to proceed. */
    if (!(key->mode & REDISMODULE_WRITE) || key->value)
        return REDISMODULE_ERR;

    switch(type) {
    case REDISMODULE_KEYTYPE_LIST:
        obj = createQuicklistObject();
        quicklistSetOptions(obj->ptr, server.list_max_ziplist_size,
                            server.list_compress_depth);
        break;
    case REDISMODULE_KEYTYPE_ZSET:
        obj = createZsetZiplistObject();
        break;
    case REDISMODULE_KEYTYPE_HASH:
        obj = createHashObject();
        break;
    default: return REDISMODULE_ERR;
    }
    dbAdd(key->db,key->key,obj);
    key->value = obj;
    return REDISMODULE_OK;
}

/* This function is called in low-level API implementation functions in order
 * to check if the value associated with the key remained empty after an
 * operation that removed elements from an aggregate data type.
 *
 * If this happens, the key is deleted from the DB and the key object state
 * is set to the right one in order to be targeted again by write operations
 * possibly recreating the key if needed.
 *
 * The function returns 1 if the key value object is found empty and is
 * deleted, otherwise 0 is returned. */
int moduleDelKeyIfEmpty(RedisModuleKey *key) {
    if (!(key->mode & REDISMODULE_WRITE) || key->value == NULL) return 0;
    int isempty;
    robj *o = key->value;

    switch(o->type) {
    case OBJ_LIST: isempty = listTypeLength(o) == 0; break;
    case OBJ_SET: isempty = setTypeSize(o) == 0; break;
    case OBJ_ZSET: isempty = zsetLength(o) == 0; break;
    case OBJ_HASH : isempty = hashTypeLength(o) == 0; break;
    default: isempty = 0;
    }

    if (isempty) {
        dbDelete(key->db,key->key);
        key->value = NULL;
        return 1;
    } else {
        return 0;
    }
}

/* --------------------------------------------------------------------------
 * Service API exported to modules
 *
 * Note that all the exported APIs are called RM_<funcname> in the core
 * and RedisModule_<funcname> in the module side (defined as function
 * pointers in redismodule.h). In this way the dynamic linker does not
 * mess with our global function pointers, overriding it with the symbols
 * defined in the main executable having the same names.
 * -------------------------------------------------------------------------- */

/* Lookup the requested module API and store the function pointer into the
 * target pointer. The function returns REDISMODULE_ERR if there is no such
 * named API, otherwise REDISMODULE_OK.
 *
 * This function is not meant to be used by modules developer, it is only
 * used implicitly by including redismodule.h. */
int RM_GetApi(const char *funcname, void **targetPtrPtr) {
    dictEntry *he = dictFind(server.moduleapi, funcname);
    if (!he) return REDISMODULE_ERR;
    *targetPtrPtr = dictGetVal(he);
    return REDISMODULE_OK;
}

/* Free the context after the user function was called. */
void moduleFreeContext(RedisModuleCtx *ctx) {
    autoMemoryCollect(ctx);
    poolAllocRelease(ctx);
    if (ctx->postponed_arrays) {
        zfree(ctx->postponed_arrays);
        ctx->postponed_arrays_count = 0;
        serverLog(LL_WARNING,
            "API misuse detected in module %s: "
            "RedisModule_ReplyWithArray(REDISMODULE_POSTPONED_ARRAY_LEN) "
            "not matched by the same number of RedisModule_SetReplyArrayLen() "
            "calls.",
            ctx->module->name);
    }
}

/* Helper function for when a command callback is called, in order to handle
 * details needed to correctly replicate commands. */
void moduleHandlePropagationAfterCommandCallback(RedisModuleCtx *ctx) {
    client *c = ctx->client;

    /* We don't want any automatic propagation here since in modules we handle
     * replication / AOF propagation in explicit ways. */
    preventCommandPropagation(c);

    /* Handle the replication of the final EXEC, since whatever a command
     * emits is always wrappered around MULTI/EXEC. */
    if (ctx->flags & REDISMODULE_CTX_MULTI_EMITTED) {
        robj *propargv[1];
        propargv[0] = createStringObject("EXEC",4);
        alsoPropagate(server.execCommand,c->db->id,propargv,1,
            PROPAGATE_AOF|PROPAGATE_REPL);
        decrRefCount(propargv[0]);
    }
}

/* This Redis command binds the normal Redis command invocation with commands
 * exported by modules. */
void RedisModuleCommandDispatcher(client *c) {
    RedisModuleCommandProxy *cp = (void*)(unsigned long)c->cmd->getkeys_proc;
    RedisModuleCtx ctx = REDISMODULE_CTX_INIT;

    ctx.module = cp->module;
    ctx.client = c;
    cp->func(&ctx,(void**)c->argv,c->argc);
    moduleHandlePropagationAfterCommandCallback(&ctx);
    moduleFreeContext(&ctx);
}

/* This function returns the list of keys, with the same interface as the
 * 'getkeys' function of the native commands, for module commands that exported
 * the "getkeys-api" flag during the registration. This is done when the
 * list of keys are not at fixed positions, so that first/last/step cannot
 * be used.
 *
 * In order to accomplish its work, the module command is called, flagging
 * the context in a way that the command can recognize this is a special
 * "get keys" call by calling RedisModule_IsKeysPositionRequest(ctx). */
int *moduleGetCommandKeysViaAPI(struct redisCommand *cmd, robj **argv, int argc, int *numkeys) {
    RedisModuleCommandProxy *cp = (void*)(unsigned long)cmd->getkeys_proc;
    RedisModuleCtx ctx = REDISMODULE_CTX_INIT;

    ctx.module = cp->module;
    ctx.client = NULL;
    ctx.flags |= REDISMODULE_CTX_KEYS_POS_REQUEST;
    cp->func(&ctx,(void**)argv,argc);
    int *res = ctx.keys_pos;
    if (numkeys) *numkeys = ctx.keys_count;
    moduleFreeContext(&ctx);
    return res;
}

/* Return non-zero if a module command, that was declared with the
 * flag "getkeys-api", is called in a special way to get the keys positions
 * and not to get executed. Otherwise zero is returned. */
int RM_IsKeysPositionRequest(RedisModuleCtx *ctx) {
    return (ctx->flags & REDISMODULE_CTX_KEYS_POS_REQUEST) != 0;
}

/* When a module command is called in order to obtain the position of
 * keys, since it was flagged as "getkeys-api" during the registration,
 * the command implementation checks for this special call using the
 * RedisModule_IsKeysPositionRequest() API and uses this function in
 * order to report keys, like in the following example:
 *
 *  if (RedisModule_IsKeysPositionRequest(ctx)) {
 *      RedisModule_KeyAtPos(ctx,1);
 *      RedisModule_KeyAtPos(ctx,2);
 *  }
 *
 *  Note: in the example below the get keys API would not be needed since
 *  keys are at fixed positions. This interface is only used for commands
 *  with a more complex structure. */
void RM_KeyAtPos(RedisModuleCtx *ctx, int pos) {
    if (!(ctx->flags & REDISMODULE_CTX_KEYS_POS_REQUEST)) return;
    if (pos <= 0) return;
    ctx->keys_pos = zrealloc(ctx->keys_pos,sizeof(int)*(ctx->keys_count+1));
    ctx->keys_pos[ctx->keys_count++] = pos;
}

/* Helper for RM_CreateCommand(). Truns a string representing command
 * flags into the command flags used by the Redis core.
 *
 * It returns the set of flags, or -1 if unknown flags are found. */
int commandFlagsFromString(char *s) {
    int count, j;
    int flags = 0;
    sds *tokens = sdssplitlen(s,strlen(s)," ",1,&count);
    for (j = 0; j < count; j++) {
        char *t = tokens[j];
        if (!strcasecmp(t,"write")) flags |= CMD_WRITE;
        else if (!strcasecmp(t,"readonly")) flags |= CMD_READONLY;
        else if (!strcasecmp(t,"admin")) flags |= CMD_ADMIN;
        else if (!strcasecmp(t,"deny-oom")) flags |= CMD_DENYOOM;
        else if (!strcasecmp(t,"deny-script")) flags |= CMD_NOSCRIPT;
        else if (!strcasecmp(t,"allow-loading")) flags |= CMD_LOADING;
        else if (!strcasecmp(t,"pubsub")) flags |= CMD_PUBSUB;
        else if (!strcasecmp(t,"random")) flags |= CMD_RANDOM;
        else if (!strcasecmp(t,"allow-stale")) flags |= CMD_STALE;
        else if (!strcasecmp(t,"no-monitor")) flags |= CMD_SKIP_MONITOR;
        else if (!strcasecmp(t,"fast")) flags |= CMD_FAST;
        else if (!strcasecmp(t,"getkeys-api")) flags |= CMD_MODULE_GETKEYS;
        else if (!strcasecmp(t,"no-cluster")) flags |= CMD_MODULE_NO_CLUSTER;
        else break;
    }
    sdsfreesplitres(tokens,count);
    if (j != count) return -1; /* Some token not processed correctly. */
    return flags;
}

/* Register a new command in the Redis server, that will be handled by
 * calling the function pointer 'func' using the RedisModule calling
 * convention. The function returns REDISMODULE_ERR if the specified command
 * name is already busy or a set of invalid flags were passed, otherwise
 * REDISMODULE_OK is returned and the new command is registered.
 *
 * This function must be called during the initialization of the module
 * inside the RedisModule_OnLoad() function. Calling this function outside
 * of the initialization function is not defined.
 *
 * The command function type is the following:
 *
 *      int MyCommand_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc);
 *
 * And is supposed to always return REDISMODULE_OK.
 *
 * The set of flags 'strflags' specify the behavior of the command, and should
 * be passed as a C string compoesd of space separated words, like for
 * example "write deny-oom". The set of flags are:
 *
 * * **"write"**:     The command may modify the data set (it may also read
 *                    from it).
 * * **"readonly"**:  The command returns data from keys but never writes.
 * * **"admin"**:     The command is an administrative command (may change
 *                    replication or perform similar tasks).
 * * **"deny-oom"**:  The command may use additional memory and should be
 *                    denied during out of memory conditions.
 * * **"deny-script"**:   Don't allow this command in Lua scripts.
 * * **"allow-loading"**: Allow this command while the server is loading data.
 *                        Only commands not interacting with the data set
 *                        should be allowed to run in this mode. If not sure
 *                        don't use this flag.
 * * **"pubsub"**:    The command publishes things on Pub/Sub channels.
 * * **"random"**:    The command may have different outputs even starting
 *                    from the same input arguments and key values.
 * * **"allow-stale"**: The command is allowed to run on slaves that don't
 *                      serve stale data. Don't use if you don't know what
 *                      this means.
 * * **"no-monitor"**: Don't propoagate the command on monitor. Use this if
 *                     the command has sensible data among the arguments.
 * * **"fast"**:      The command time complexity is not greater
 *                    than O(log(N)) where N is the size of the collection or
 *                    anything else representing the normal scalability
 *                    issue with the command.
 * * **"getkeys-api"**: The command implements the interface to return
 *                      the arguments that are keys. Used when start/stop/step
 *                      is not enough because of the command syntax.
 * * **"no-cluster"**: The command should not register in Redis Cluster
 *                     since is not designed to work with it because, for
 *                     example, is unable to report the position of the
 *                     keys, programmatically creates key names, or any
 *                     other reason.
 */
int RM_CreateCommand(RedisModuleCtx *ctx, const char *name, RedisModuleCmdFunc cmdfunc, const char *strflags, int firstkey, int lastkey, int keystep) {
    int flags = strflags ? commandFlagsFromString((char*)strflags) : 0;
    if (flags == -1) return REDISMODULE_ERR;
    if ((flags & CMD_MODULE_NO_CLUSTER) && server.cluster_enabled)
        return REDISMODULE_ERR;

    struct redisCommand *rediscmd;
    RedisModuleCommandProxy *cp;
    sds cmdname = sdsnew(name);

    /* Check if the command name is busy. */
    if (lookupCommand((char*)name) != NULL) {
        sdsfree(cmdname);
        return REDISMODULE_ERR;
    }

    /* Create a command "proxy", which is a structure that is referenced
     * in the command table, so that the generic command that works as
     * binding between modules and Redis, can know what function to call
     * and what the module is.
     *
     * Note that we use the Redis command table 'getkeys_proc' in order to
     * pass a reference to the command proxy structure. */
    cp = zmalloc(sizeof(*cp));
    cp->module = ctx->module;
    cp->func = cmdfunc;
    cp->rediscmd = zmalloc(sizeof(*rediscmd));
    cp->rediscmd->name = cmdname;
    cp->rediscmd->proc = RedisModuleCommandDispatcher;
    cp->rediscmd->arity = -1;
    cp->rediscmd->flags = flags | CMD_MODULE;
    cp->rediscmd->getkeys_proc = (redisGetKeysProc*)(unsigned long)cp;
    cp->rediscmd->firstkey = firstkey;
    cp->rediscmd->lastkey = lastkey;
    cp->rediscmd->keystep = keystep;
    cp->rediscmd->microseconds = 0;
    cp->rediscmd->calls = 0;
    dictAdd(server.commands,sdsdup(cmdname),cp->rediscmd);
    dictAdd(server.orig_commands,sdsdup(cmdname),cp->rediscmd);
    return REDISMODULE_OK;
}

/* Called by RM_Init() to setup the `ctx->module` structure.
 *
 * This is an internal function, Redis modules developers don't need
 * to use it. */
void RM_SetModuleAttribs(RedisModuleCtx *ctx, const char *name, int ver, int apiver){
    RedisModule *module;

    if (ctx->module != NULL) return;
    module = zmalloc(sizeof(*module));
    module->name = sdsnew((char*)name);
    module->ver = ver;
    module->apiver = apiver;
    module->types = listCreate();
    ctx->module = module;
}

/* Return the current UNIX time in milliseconds. */
long long RM_Milliseconds(void) {
    return mstime();
}

/* --------------------------------------------------------------------------
 * Automatic memory management for modules
 * -------------------------------------------------------------------------- */

/* Enable automatic memory management. See API.md for more information.
 *
 * The function must be called as the first function of a command implementation
 * that wants to use automatic memory. */
void RM_AutoMemory(RedisModuleCtx *ctx) {
    ctx->flags |= REDISMODULE_CTX_AUTO_MEMORY;
}

/* Add a new object to release automatically when the callback returns. */
void autoMemoryAdd(RedisModuleCtx *ctx, int type, void *ptr) {
    if (!(ctx->flags & REDISMODULE_CTX_AUTO_MEMORY)) return;
    if (ctx->amqueue_used == ctx->amqueue_len) {
        ctx->amqueue_len *= 2;
        if (ctx->amqueue_len < 16) ctx->amqueue_len = 16;
        ctx->amqueue = zrealloc(ctx->amqueue,sizeof(struct AutoMemEntry)*ctx->amqueue_len);
    }
    ctx->amqueue[ctx->amqueue_used].type = type;
    ctx->amqueue[ctx->amqueue_used].ptr = ptr;
    ctx->amqueue_used++;
}

/* Mark an object as freed in the auto release queue, so that users can still
 * free things manually if they want.
 *
 * The function returns 1 if the object was actually found in the auto memory
 * pool, otherwise 0 is returned. */
int autoMemoryFreed(RedisModuleCtx *ctx, int type, void *ptr) {
    if (!(ctx->flags & REDISMODULE_CTX_AUTO_MEMORY)) return 0;

    int count = (ctx->amqueue_used+1)/2;
    for (int j = 0; j < count; j++) {
        for (int side = 0; side < 2; side++) {
            /* For side = 0 check right side of the array, for
             * side = 1 check the left side instead (zig-zag scanning). */
            int i = (side == 0) ? (ctx->amqueue_used - 1 - j) : j;
            if (ctx->amqueue[i].type == type &&
                ctx->amqueue[i].ptr == ptr)
            {
                ctx->amqueue[i].type = REDISMODULE_AM_FREED;

                /* Switch the freed element and the last element, to avoid growing
                 * the queue unnecessarily if we allocate/free in a loop */
                if (i != ctx->amqueue_used-1) {
                    ctx->amqueue[i] = ctx->amqueue[ctx->amqueue_used-1];
                }

                /* Reduce the size of the queue because we either moved the top
                 * element elsewhere or freed it */
                ctx->amqueue_used--;
                return 1;
            }
        }
    }
    return 0;
}

/* Release all the objects in queue. */
void autoMemoryCollect(RedisModuleCtx *ctx) {
    if (!(ctx->flags & REDISMODULE_CTX_AUTO_MEMORY)) return;
    /* Clear the AUTO_MEMORY flag from the context, otherwise the functions
     * we call to free the resources, will try to scan the auto release
     * queue to mark the entries as freed. */
    ctx->flags &= ~REDISMODULE_CTX_AUTO_MEMORY;
    int j;
    for (j = 0; j < ctx->amqueue_used; j++) {
        void *ptr = ctx->amqueue[j].ptr;
        switch(ctx->amqueue[j].type) {
        case REDISMODULE_AM_STRING: decrRefCount(ptr); break;
        case REDISMODULE_AM_REPLY: RM_FreeCallReply(ptr); break;
        case REDISMODULE_AM_KEY: RM_CloseKey(ptr); break;
        }
    }
    ctx->flags |= REDISMODULE_CTX_AUTO_MEMORY;
    zfree(ctx->amqueue);
    ctx->amqueue = NULL;
    ctx->amqueue_len = 0;
    ctx->amqueue_used = 0;
}

/* --------------------------------------------------------------------------
 * String objects APIs
 * -------------------------------------------------------------------------- */

/* Create a new module string object. The returned string must be freed
 * with RedisModule_FreeString(), unless automatic memory is enabled.
 *
 * The string is created by copying the `len` bytes starting
 * at `ptr`. No reference is retained to the passed buffer. */
RedisModuleString *RM_CreateString(RedisModuleCtx *ctx, const char *ptr, size_t len) {
    RedisModuleString *o = createStringObject(ptr,len);
    autoMemoryAdd(ctx,REDISMODULE_AM_STRING,o);
    return o;
}


/* Create a new module string object from a printf format and arguments.
 * The returned string must be freed with RedisModule_FreeString(), unless
 * automatic memory is enabled.
 *
 * The string is created using the sds formatter function sdscatvprintf(). */
RedisModuleString *RM_CreateStringPrintf(RedisModuleCtx *ctx, const char *fmt, ...) {
    sds s = sdsempty();

    va_list ap;
    va_start(ap, fmt);
    s = sdscatvprintf(s, fmt, ap);
    va_end(ap);

    RedisModuleString *o = createObject(OBJ_STRING, s);
    autoMemoryAdd(ctx,REDISMODULE_AM_STRING,o);

    return o;
}


/* Like RedisModule_CreatString(), but creates a string starting from a long long
 * integer instead of taking a buffer and its length.
 *
 * The returned string must be released with RedisModule_FreeString() or by
 * enabling automatic memory management. */
RedisModuleString *RM_CreateStringFromLongLong(RedisModuleCtx *ctx, long long ll) {
    char buf[LONG_STR_SIZE];
    size_t len = ll2string(buf,sizeof(buf),ll);
    return RM_CreateString(ctx,buf,len);
}

/* Like RedisModule_CreatString(), but creates a string starting from another
 * RedisModuleString.
 *
 * The returned string must be released with RedisModule_FreeString() or by
 * enabling automatic memory management. */
RedisModuleString *RM_CreateStringFromString(RedisModuleCtx *ctx, const RedisModuleString *str) {
    RedisModuleString *o = dupStringObject(str);
    autoMemoryAdd(ctx,REDISMODULE_AM_STRING,o);
    return o;
}

/* Free a module string object obtained with one of the Redis modules API calls
 * that return new string objects.
 *
 * It is possible to call this function even when automatic memory management
 * is enabled. In that case the string will be released ASAP and removed
 * from the pool of string to release at the end. */
void RM_FreeString(RedisModuleCtx *ctx, RedisModuleString *str) {
    decrRefCount(str);
    autoMemoryFreed(ctx,REDISMODULE_AM_STRING,str);
}

/* Every call to this function, will make the string 'str' requiring
 * an additional call to RedisModule_FreeString() in order to really
 * free the string. Note that the automatic freeing of the string obtained
 * enabling modules automatic memory management counts for one
 * RedisModule_FreeString() call (it is just executed automatically).
 *
 * Normally you want to call this function when, at the same time
 * the following conditions are true:
 *
 * 1) You have automatic memory management enabled.
 * 2) You want to create string objects.
 * 3) Those string objects you create need to live *after* the callback
 *    function(for example a command implementation) creating them returns.
 *
 * Usually you want this in order to store the created string object
 * into your own data structure, for example when implementing a new data
 * type.
 *
 * Note that when memory management is turned off, you don't need
 * any call to RetainString() since creating a string will always result
 * into a string that lives after the callback function returns, if
 * no FreeString() call is performed. */
void RM_RetainString(RedisModuleCtx *ctx, RedisModuleString *str) {
    if (!autoMemoryFreed(ctx,REDISMODULE_AM_STRING,str)) {
        /* Increment the string reference counting only if we can't
         * just remove the object from the list of objects that should
         * be reclaimed. Why we do that, instead of just incrementing
         * the refcount in any case, and let the automatic FreeString()
         * call at the end to bring the refcount back at the desired
         * value? Because this way we ensure that the object refcount
         * value is 1 (instead of going to 2 to be dropped later to 1)
         * after the call to this function. This is needed for functions
         * like RedisModule_StringAppendBuffer() to work. */
        incrRefCount(str);
    }
}

/* Given a string module object, this function returns the string pointer
 * and length of the string. The returned pointer and length should only
 * be used for read only accesses and never modified. */
const char *RM_StringPtrLen(const RedisModuleString *str, size_t *len) {
    if (str == NULL) {
        const char *errmsg = "(NULL string reply referenced in module)";
        if (len) *len = strlen(errmsg);
        return errmsg;
    }
    if (len) *len = sdslen(str->ptr);
    return str->ptr;
}

/* --------------------------------------------------------------------------
 * Higher level string operations
 * ------------------------------------------------------------------------- */

/* Convert the string into a long long integer, storing it at `*ll`.
 * Returns REDISMODULE_OK on success. If the string can't be parsed
 * as a valid, strict long long (no spaces before/after), REDISMODULE_ERR
 * is returned. */
int RM_StringToLongLong(const RedisModuleString *str, long long *ll) {
    return string2ll(str->ptr,sdslen(str->ptr),ll) ? REDISMODULE_OK :
                                                     REDISMODULE_ERR;
}

/* Convert the string into a double, storing it at `*d`.
 * Returns REDISMODULE_OK on success or REDISMODULE_ERR if the string is
 * not a valid string representation of a double value. */
int RM_StringToDouble(const RedisModuleString *str, double *d) {
    int retval = getDoubleFromObject(str,d);
    return (retval == C_OK) ? REDISMODULE_OK : REDISMODULE_ERR;
}

/* Compare two string objects, returning -1, 0 or 1 respectively if
 * a < b, a == b, a > b. Strings are compared byte by byte as two
 * binary blobs without any encoding care / collation attempt. */
int RM_StringCompare(RedisModuleString *a, RedisModuleString *b) {
    return compareStringObjects(a,b);
}

/* Return the (possibly modified in encoding) input 'str' object if
 * the string is unshared, otherwise NULL is returned. */
RedisModuleString *moduleAssertUnsharedString(RedisModuleString *str) {
    if (str->refcount != 1) {
        serverLog(LL_WARNING,
            "Module attempted to use an in-place string modify operation "
            "with a string referenced multiple times. Please check the code "
            "for API usage correctness.");
        return NULL;
    }
    if (str->encoding == OBJ_ENCODING_EMBSTR) {
        /* Note: here we "leak" the additional allocation that was
         * used in order to store the embedded string in the object. */
        str->ptr = sdsnewlen(str->ptr,sdslen(str->ptr));
        str->encoding = OBJ_ENCODING_RAW;
    } else if (str->encoding == OBJ_ENCODING_INT) {
        /* Convert the string from integer to raw encoding. */
        str->ptr = sdsfromlonglong((long)str->ptr);
        str->encoding = OBJ_ENCODING_RAW;
    }
    return str;
}

/* Append the specified buffere to the string 'str'. The string must be a
 * string created by the user that is referenced only a single time, otherwise
 * REDISMODULE_ERR is returend and the operation is not performed. */
int RM_StringAppendBuffer(RedisModuleCtx *ctx, RedisModuleString *str, const char *buf, size_t len) {
    UNUSED(ctx);
    str = moduleAssertUnsharedString(str);
    if (str == NULL) return REDISMODULE_ERR;
    str->ptr = sdscatlen(str->ptr,buf,len);
    return REDISMODULE_OK;
}

/* --------------------------------------------------------------------------
 * Reply APIs
 *
 * Most functions always return REDISMODULE_OK so you can use it with
 * 'return' in order to return from the command implementation with:
 *
 * if (... some condition ...)
 *     return RM_ReplyWithLongLong(ctx,mycount);
 * -------------------------------------------------------------------------- */

/* Send an error about the number of arguments given to the command,
 * citing the command name in the error message.
 *
 * Example:
 *
 *  if (argc != 3) return RedisModule_WrongArity(ctx);
 */
int RM_WrongArity(RedisModuleCtx *ctx) {
    addReplyErrorFormat(ctx->client,
        "wrong number of arguments for '%s' command",
        (char*)ctx->client->argv[0]->ptr);
    return REDISMODULE_OK;
}

/* Send an integer reply to the client, with the specified long long value.
 * The function always returns REDISMODULE_OK. */
int RM_ReplyWithLongLong(RedisModuleCtx *ctx, long long ll) {
    addReplyLongLong(ctx->client,ll);
    return REDISMODULE_OK;
}

/* Reply with an error or simple string (status message). Used to implement
 * ReplyWithSimpleString() and ReplyWithError().
 * The function always returns REDISMODULE_OK. */
int replyWithStatus(RedisModuleCtx *ctx, const char *msg, char *prefix) {
    sds strmsg = sdsnewlen(prefix,1);
    strmsg = sdscat(strmsg,msg);
    strmsg = sdscatlen(strmsg,"\r\n",2);
    addReplySds(ctx->client,strmsg);
    return REDISMODULE_OK;
}

/* Reply with the error 'err'.
 *
 * Note that 'err' must contain all the error, including
 * the initial error code. The function only provides the initial "-", so
 * the usage is, for example:
 *
 *  RM_ReplyWithError(ctx,"ERR Wrong Type");
 *
 * and not just:
 *
 *  RM_ReplyWithError(ctx,"Wrong Type");
 *
 * The function always returns REDISMODULE_OK.
 */
int RM_ReplyWithError(RedisModuleCtx *ctx, const char *err) {
    return replyWithStatus(ctx,err,"-");
}

/* Reply with a simple string (+... \r\n in RESP protocol). This replies
 * are suitable only when sending a small non-binary string with small
 * overhead, like "OK" or similar replies.
 *
 * The function always returns REDISMODULE_OK. */
int RM_ReplyWithSimpleString(RedisModuleCtx *ctx, const char *msg) {
    return replyWithStatus(ctx,msg,"+");
}

/* Reply with an array type of 'len' elements. However 'len' other calls
 * to `ReplyWith*` style functions must follow in order to emit the elements
 * of the array.
 *
 * When producing arrays with a number of element that is not known beforehand
 * the function can be called with the special count
 * REDISMODULE_POSTPONED_ARRAY_LEN, and the actual number of elements can be
 * later set with RedisModule_ReplySetArrayLength() (which will set the
 * latest "open" count if there are multiple ones).
 *
 * The function always returns REDISMODULE_OK. */
int RM_ReplyWithArray(RedisModuleCtx *ctx, long len) {
    if (len == REDISMODULE_POSTPONED_ARRAY_LEN) {
        ctx->postponed_arrays = zrealloc(ctx->postponed_arrays,sizeof(void*)*
                (ctx->postponed_arrays_count+1));
        ctx->postponed_arrays[ctx->postponed_arrays_count] =
            addDeferredMultiBulkLength(ctx->client);
        ctx->postponed_arrays_count++;
    } else {
        addReplyMultiBulkLen(ctx->client,len);
    }
    return REDISMODULE_OK;
}

/* When RedisModule_ReplyWithArray() is used with the argument
 * REDISMODULE_POSTPONED_ARRAY_LEN, because we don't know beforehand the number
 * of items we are going to output as elements of the array, this function
 * will take care to set the array length.
 *
 * Since it is possible to have multiple array replies pending with unknown
 * length, this function guarantees to always set the latest array length
 * that was created in a postponed way.
 *
 * For example in order to output an array like [1,[10,20,30]] we
 * could write:
 *
 *  RedisModule_ReplyWithArray(ctx,REDISMODULE_POSTPONED_ARRAY_LEN);
 *  RedisModule_ReplyWithLongLong(ctx,1);
 *  RedisModule_ReplyWithArray(ctx,REDISMODULE_POSTPONED_ARRAY_LEN);
 *  RedisModule_ReplyWithLongLong(ctx,10);
 *  RedisModule_ReplyWithLongLong(ctx,20);
 *  RedisModule_ReplyWithLongLong(ctx,30);
 *  RedisModule_ReplySetArrayLength(ctx,3); // Set len of 10,20,30 array.
 *  RedisModule_ReplySetArrayLength(ctx,2); // Set len of top array
 *
 * Note that in the above example there is no reason to postpone the array
 * length, since we produce a fixed number of elements, but in the practice
 * the code may use an interator or other ways of creating the output so
 * that is not easy to calculate in advance the number of elements.
 */
void RM_ReplySetArrayLength(RedisModuleCtx *ctx, long len) {
    if (ctx->postponed_arrays_count == 0) {
        serverLog(LL_WARNING,
            "API misuse detected in module %s: "
            "RedisModule_ReplySetArrayLength() called without previous "
            "RedisModule_ReplyWithArray(ctx,REDISMODULE_POSTPONED_ARRAY_LEN) "
            "call.", ctx->module->name);
            return;
    }
    ctx->postponed_arrays_count--;
    setDeferredMultiBulkLength(ctx->client,
            ctx->postponed_arrays[ctx->postponed_arrays_count],
            len);
    if (ctx->postponed_arrays_count == 0) {
        zfree(ctx->postponed_arrays);
        ctx->postponed_arrays = NULL;
    }
}

/* Reply with a bulk string, taking in input a C buffer pointer and length.
 *
 * The function always returns REDISMODULE_OK. */
int RM_ReplyWithStringBuffer(RedisModuleCtx *ctx, const char *buf, size_t len) {
    addReplyBulkCBuffer(ctx->client,(char*)buf,len);
    return REDISMODULE_OK;
}

/* Reply with a bulk string, taking in input a RedisModuleString object.
 *
 * The function always returns REDISMODULE_OK. */
int RM_ReplyWithString(RedisModuleCtx *ctx, RedisModuleString *str) {
    addReplyBulk(ctx->client,str);
    return REDISMODULE_OK;
}

/* Reply to the client with a NULL. In the RESP protocol a NULL is encoded
 * as the string "$-1\r\n".
 *
 * The function always returns REDISMODULE_OK. */
int RM_ReplyWithNull(RedisModuleCtx *ctx) {
    addReply(ctx->client,shared.nullbulk);
    return REDISMODULE_OK;
}

/* Reply exactly what a Redis command returned us with RedisModule_Call().
 * This function is useful when we use RedisModule_Call() in order to
 * execute some command, as we want to reply to the client exactly the
 * same reply we obtained by the command.
 *
 * The function always returns REDISMODULE_OK. */
int RM_ReplyWithCallReply(RedisModuleCtx *ctx, RedisModuleCallReply *reply) {
    sds proto = sdsnewlen(reply->proto, reply->protolen);
    addReplySds(ctx->client,proto);
    return REDISMODULE_OK;
}

/* Send a string reply obtained converting the double 'd' into a bulk string.
 * This function is basically equivalent to converting a double into
 * a string into a C buffer, and then calling the function
 * RedisModule_ReplyWithStringBuffer() with the buffer and length.
 *
 * The function always returns REDISMODULE_OK. */
int RM_ReplyWithDouble(RedisModuleCtx *ctx, double d) {
    addReplyDouble(ctx->client,d);
    return REDISMODULE_OK;
}

/* --------------------------------------------------------------------------
 * Commands replication API
 * -------------------------------------------------------------------------- */

/* Helper function to replicate MULTI the first time we replicate something
 * in the context of a command execution. EXEC will be handled by the
 * RedisModuleCommandDispatcher() function. */
void moduleReplicateMultiIfNeeded(RedisModuleCtx *ctx) {
    if (ctx->flags & REDISMODULE_CTX_MULTI_EMITTED) return;
    execCommandPropagateMulti(ctx->client);
    ctx->flags |= REDISMODULE_CTX_MULTI_EMITTED;
}

/* Replicate the specified command and arguments to slaves and AOF, as effect
 * of execution of the calling command implementation.
 *
 * The replicated commands are always wrapped into the MULTI/EXEC that
 * contains all the commands replicated in a given module command
 * execution. However the commands replicated with RedisModule_Call()
 * are the first items, the ones replicated with RedisModule_Replicate()
 * will all follow before the EXEC.
 *
 * Modules should try to use one interface or the other.
 *
 * This command follows exactly the same interface of RedisModule_Call(),
 * so a set of format specifiers must be passed, followed by arguments
 * matching the provided format specifiers.
 *
 * Please refer to RedisModule_Call() for more information.
 *
 * The command returns REDISMODULE_ERR if the format specifiers are invalid
 * or the command name does not belong to a known command. */
int RM_Replicate(RedisModuleCtx *ctx, const char *cmdname, const char *fmt, ...) {
    struct redisCommand *cmd;
    robj **argv = NULL;
    int argc = 0, flags = 0, j;
    va_list ap;

    cmd = lookupCommandByCString((char*)cmdname);
    if (!cmd) return REDISMODULE_ERR;

    /* Create the client and dispatch the command. */
    va_start(ap, fmt);
    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,&flags,ap);
    va_end(ap);
    if (argv == NULL) return REDISMODULE_ERR;

    /* Replicate! */
    moduleReplicateMultiIfNeeded(ctx);
    alsoPropagate(cmd,ctx->client->db->id,argv,argc,
        PROPAGATE_AOF|PROPAGATE_REPL);

    /* Release the argv. */
    for (j = 0; j < argc; j++) decrRefCount(argv[j]);
    zfree(argv);
    return REDISMODULE_OK;
}

/* This function will replicate the command exactly as it was invoked
 * by the client. Note that this function will not wrap the command into
 * a MULTI/EXEC stanza, so it should not be mixed with other replication
 * commands.
 *
 * Basically this form of replication is useful when you want to propagate
 * the command to the slaves and AOF file exactly as it was called, since
 * the command can just be re-executed to deterministically re-create the
 * new state starting from the old one.
 *
 * The function always returns REDISMODULE_OK. */
int RM_ReplicateVerbatim(RedisModuleCtx *ctx) {
    alsoPropagate(ctx->client->cmd,ctx->client->db->id,
        ctx->client->argv,ctx->client->argc,
        PROPAGATE_AOF|PROPAGATE_REPL);
    return REDISMODULE_OK;
}

/* --------------------------------------------------------------------------
 * DB and Key APIs -- Generic API
 * -------------------------------------------------------------------------- */

/* Return the ID of the current client calling the currently active module
 * command. The returned ID has a few guarantees:
 *
 * 1. The ID is different for each different client, so if the same client
 *    executes a module command multiple times, it can be recognized as
 *    having the same ID, otherwise the ID will be different.
 * 2. The ID increases monotonically. Clients connecting to the server later
 *    are guaranteed to get IDs greater than any past ID previously seen.
 *
 * Valid IDs are from 1 to 2^64-1. If 0 is returned it means there is no way
 * to fetch the ID in the context the function was currently called. */
unsigned long long RM_GetClientId(RedisModuleCtx *ctx) {
    if (ctx->client == NULL) return 0;
    return ctx->client->id;
}

/* Return the currently selected DB. */
int RM_GetSelectedDb(RedisModuleCtx *ctx) {
    return ctx->client->db->id;
}

/* Change the currently selected DB. Returns an error if the id
 * is out of range.
 *
 * Note that the client will retain the currently selected DB even after
 * the Redis command implemented by the module calling this function
 * returns.
 *
 * If the module command wishes to change something in a different DB and
 * returns back to the original one, it should call RedisModule_GetSelectedDb()
 * before in order to restore the old DB number before returning. */
int RM_SelectDb(RedisModuleCtx *ctx, int newid) {
    int retval = selectDb(ctx->client,newid);
    return (retval == C_OK) ? REDISMODULE_OK : REDISMODULE_ERR;
}

/* Return an handle representing a Redis key, so that it is possible
 * to call other APIs with the key handle as argument to perform
 * operations on the key.
 *
 * The return value is the handle repesenting the key, that must be
 * closed with RM_CloseKey().
 *
 * If the key does not exist and WRITE mode is requested, the handle
 * is still returned, since it is possible to perform operations on
 * a yet not existing key (that will be created, for example, after
 * a list push operation). If the mode is just READ instead, and the
 * key does not exist, NULL is returned. However it is still safe to
 * call RedisModule_CloseKey() and RedisModule_KeyType() on a NULL
 * value. */
void *RM_OpenKey(RedisModuleCtx *ctx, robj *keyname, int mode) {
    RedisModuleKey *kp;
    robj *value;

    if (mode & REDISMODULE_WRITE) {
        value = lookupKeyWrite(ctx->client->db,keyname);
    } else {
        value = lookupKeyRead(ctx->client->db,keyname);
        if (value == NULL) {
            return NULL;
        }
    }

    /* Setup the key handle. */
    kp = zmalloc(sizeof(*kp));
    kp->ctx = ctx;
    kp->db = ctx->client->db;
    kp->key = keyname;
    incrRefCount(keyname);
    kp->value = value;
    kp->iter = NULL;
    kp->mode = mode;
    zsetKeyReset(kp);
    autoMemoryAdd(ctx,REDISMODULE_AM_KEY,kp);
    return (void*)kp;
}

/* Close a key handle. */
void RM_CloseKey(RedisModuleKey *key) {
    if (key == NULL) return;
    if (key->mode & REDISMODULE_WRITE) signalModifiedKey(key->db,key->key);
    /* TODO: if (key->iter) RM_KeyIteratorStop(kp); */
    RM_ZsetRangeStop(key);
    decrRefCount(key->key);
    autoMemoryFreed(key->ctx,REDISMODULE_AM_KEY,key);
    zfree(key);
}

/* Return the type of the key. If the key pointer is NULL then
 * REDISMODULE_KEYTYPE_EMPTY is returned. */
int RM_KeyType(RedisModuleKey *key) {
    if (key == NULL || key->value ==  NULL) return REDISMODULE_KEYTYPE_EMPTY;
    /* We map between defines so that we are free to change the internal
     * defines as desired. */
    switch(key->value->type) {
    case OBJ_STRING: return REDISMODULE_KEYTYPE_STRING;
    case OBJ_LIST: return REDISMODULE_KEYTYPE_LIST;
    case OBJ_SET: return REDISMODULE_KEYTYPE_SET;
    case OBJ_ZSET: return REDISMODULE_KEYTYPE_ZSET;
    case OBJ_HASH: return REDISMODULE_KEYTYPE_HASH;
    case OBJ_MODULE: return REDISMODULE_KEYTYPE_MODULE;
    default: return 0;
    }
}

/* Return the length of the value associated with the key.
 * For strings this is the length of the string. For all the other types
 * is the number of elements (just counting keys for hashes).
 *
 * If the key pointer is NULL or the key is empty, zero is returned. */
size_t RM_ValueLength(RedisModuleKey *key) {
    if (key == NULL || key->value == NULL) return 0;
    switch(key->value->type) {
    case OBJ_STRING: return stringObjectLen(key->value);
    case OBJ_LIST: return listTypeLength(key->value);
    case OBJ_SET: return setTypeSize(key->value);
    case OBJ_ZSET: return zsetLength(key->value);
    case OBJ_HASH: return hashTypeLength(key->value);
    default: return 0;
    }
}

/* If the key is open for writing, remove it, and setup the key to
 * accept new writes as an empty key (that will be created on demand).
 * On success REDISMODULE_OK is returned. If the key is not open for
 * writing REDISMODULE_ERR is returned. */
int RM_DeleteKey(RedisModuleKey *key) {
    if (!(key->mode & REDISMODULE_WRITE)) return REDISMODULE_ERR;
    if (key->value) {
        dbDelete(key->db,key->key);
        key->value = NULL;
    }
    return REDISMODULE_OK;
}

/* Return the key expire value, as milliseconds of remaining TTL.
 * If no TTL is associated with the key or if the key is empty,
 * REDISMODULE_NO_EXPIRE is returned. */
mstime_t RM_GetExpire(RedisModuleKey *key) {
    mstime_t expire = getExpire(key->db,key->key);
    if (expire == -1 || key->value == NULL) return -1;
    expire -= mstime();
    return expire >= 0 ? expire : 0;
}

/* Set a new expire for the key. If the special expire
 * REDISMODULE_NO_EXPIRE is set, the expire is cancelled if there was
 * one (the same as the PERSIST command).
 *
 * Note that the expire must be provided as a positive integer representing
 * the number of milliseconds of TTL the key should have.
 *
 * The function returns REDISMODULE_OK on success or REDISMODULE_ERR if
 * the key was not open for writing or is an empty key. */
int RM_SetExpire(RedisModuleKey *key, mstime_t expire) {
    if (!(key->mode & REDISMODULE_WRITE) || key->value == NULL)
        return REDISMODULE_ERR;
    if (expire != REDISMODULE_NO_EXPIRE) {
        expire += mstime();
        setExpire(key->db,key->key,expire);
    } else {
        removeExpire(key->db,key->key);
    }
    return REDISMODULE_OK;
}

/* --------------------------------------------------------------------------
 * Key API for String type
 * -------------------------------------------------------------------------- */

/* If the key is open for writing, set the specified string 'str' as the
 * value of the key, deleting the old value if any.
 * On success REDISMODULE_OK is returned. If the key is not open for
 * writing or there is an active iterator, REDISMODULE_ERR is returned. */
int RM_StringSet(RedisModuleKey *key, RedisModuleString *str) {
    if (!(key->mode & REDISMODULE_WRITE) || key->iter) return REDISMODULE_ERR;
    RM_DeleteKey(key);
    setKey(key->db,key->key,str);
    key->value = str;
    return REDISMODULE_OK;
}

/* Prepare the key associated string value for DMA access, and returns
 * a pointer and size (by reference), that the user can use to read or
 * modify the string in-place accessing it directly via pointer.
 *
 * The 'mode' is composed by bitwise OR-ing the following flags:
 *
 * REDISMODULE_READ -- Read access
 * REDISMODULE_WRITE -- Write access
 *
 * If the DMA is not requested for writing, the pointer returned should
 * only be accessed in a read-only fashion.
 *
 * On error (wrong type) NULL is returned.
 *
 * DMA access rules:
 *
 * 1. No other key writing function should be called since the moment
 * the pointer is obtained, for all the time we want to use DMA access
 * to read or modify the string.
 *
 * 2. Each time RM_StringTruncate() is called, to continue with the DMA
 * access, RM_StringDMA() should be called again to re-obtain
 * a new pointer and length.
 *
 * 3. If the returned pointer is not NULL, but the length is zero, no
 * byte can be touched (the string is empty, or the key itself is empty)
 * so a RM_StringTruncate() call should be used if there is to enlarge
 * the string, and later call StringDMA() again to get the pointer.
 */
char *RM_StringDMA(RedisModuleKey *key, size_t *len, int mode) {
    /* We need to return *some* pointer for empty keys, we just return
     * a string literal pointer, that is the advantage to be mapped into
     * a read only memory page, so the module will segfault if a write
     * attempt is performed. */
    char *emptystring = "<dma-empty-string>";
    if (key->value == NULL) {
        *len = 0;
        return emptystring;
    }

    if (key->value->type != OBJ_STRING) return NULL;

    /* For write access, and even for read access if the object is encoded,
     * we unshare the string (that has the side effect of decoding it). */
    if ((mode & REDISMODULE_WRITE) || key->value->encoding != OBJ_ENCODING_RAW)
        key->value = dbUnshareStringValue(key->db, key->key, key->value);

    *len = sdslen(key->value->ptr);
    return key->value->ptr;
}

/* If the string is open for writing and is of string type, resize it, padding
 * with zero bytes if the new length is greater than the old one.
 *
 * After this call, RM_StringDMA() must be called again to continue
 * DMA access with the new pointer.
 *
 * The function returns REDISMODULE_OK on success, and REDISMODULE_ERR on
 * error, that is, the key is not open for writing, is not a string
 * or resizing for more than 512 MB is requested.
 *
 * If the key is empty, a string key is created with the new string value
 * unless the new length value requested is zero. */
int RM_StringTruncate(RedisModuleKey *key, size_t newlen) {
    if (!(key->mode & REDISMODULE_WRITE)) return REDISMODULE_ERR;
    if (key->value && key->value->type != OBJ_STRING) return REDISMODULE_ERR;
    if (newlen > 512*1024*1024) return REDISMODULE_ERR;

    /* Empty key and new len set to 0. Just return REDISMODULE_OK without
     * doing anything. */
    if (key->value == NULL && newlen == 0) return REDISMODULE_OK;

    if (key->value == NULL) {
        /* Empty key: create it with the new size. */
        robj *o = createObject(OBJ_STRING,sdsnewlen(NULL, newlen));
        setKey(key->db,key->key,o);
        key->value = o;
        decrRefCount(o);
    } else {
        /* Unshare and resize. */
        key->value = dbUnshareStringValue(key->db, key->key, key->value);
        size_t curlen = sdslen(key->value->ptr);
        if (newlen > curlen) {
            key->value->ptr = sdsgrowzero(key->value->ptr,newlen);
        } else if (newlen < curlen) {
            sdsrange(key->value->ptr,0,newlen-1);
            /* If the string is too wasteful, reallocate it. */
            if (sdslen(key->value->ptr) < sdsavail(key->value->ptr))
                key->value->ptr = sdsRemoveFreeSpace(key->value->ptr);
        }
    }
    return REDISMODULE_OK;
}

/* --------------------------------------------------------------------------
 * Key API for List type
 * -------------------------------------------------------------------------- */

/* Push an element into a list, on head or tail depending on 'where' argumnet.
 * If the key pointer is about an empty key opened for writing, the key
 * is created. On error (key opened for read-only operations or of the wrong
 * type) REDISMODULE_ERR is returned, otherwise REDISMODULE_OK is returned. */
int RM_ListPush(RedisModuleKey *key, int where, RedisModuleString *ele) {
    if (!(key->mode & REDISMODULE_WRITE)) return REDISMODULE_ERR;
    if (key->value && key->value->type != OBJ_LIST) return REDISMODULE_ERR;
    if (key->value == NULL) moduleCreateEmptyKey(key,REDISMODULE_KEYTYPE_LIST);
    listTypePush(key->value, ele,
        (where == REDISMODULE_LIST_HEAD) ? QUICKLIST_HEAD : QUICKLIST_TAIL);
    return REDISMODULE_OK;
}

/* Pop an element from the list, and returns it as a module string object
 * that the user should be free with RM_FreeString() or by enabling
 * automatic memory. 'where' specifies if the element should be popped from
 * head or tail. The command returns NULL if:
 * 1) The list is empty.
 * 2) The key was not open for writing.
 * 3) The key is not a list. */
RedisModuleString *RM_ListPop(RedisModuleKey *key, int where) {
    if (!(key->mode & REDISMODULE_WRITE) ||
        key->value == NULL ||
        key->value->type != OBJ_LIST) return NULL;
    robj *ele = listTypePop(key->value,
        (where == REDISMODULE_LIST_HEAD) ? QUICKLIST_HEAD : QUICKLIST_TAIL);
    robj *decoded = getDecodedObject(ele);
    decrRefCount(ele);
    moduleDelKeyIfEmpty(key);
    autoMemoryAdd(key->ctx,REDISMODULE_AM_STRING,decoded);
    return decoded;
}

/* --------------------------------------------------------------------------
 * Key API for Sorted Set type
 * -------------------------------------------------------------------------- */

/* Conversion from/to public flags of the Modules API and our private flags,
 * so that we have everything decoupled. */
int RM_ZsetAddFlagsToCoreFlags(int flags) {
    int retflags = 0;
    if (flags & REDISMODULE_ZADD_XX) retflags |= ZADD_XX;
    if (flags & REDISMODULE_ZADD_NX) retflags |= ZADD_NX;
    return retflags;
}

/* See previous function comment. */
int RM_ZsetAddFlagsFromCoreFlags(int flags) {
    int retflags = 0;
    if (flags & ZADD_ADDED) retflags |= REDISMODULE_ZADD_ADDED;
    if (flags & ZADD_UPDATED) retflags |= REDISMODULE_ZADD_UPDATED;
    if (flags & ZADD_NOP) retflags |= REDISMODULE_ZADD_NOP;
    return retflags;
}

/* Add a new element into a sorted set, with the specified 'score'.
 * If the element already exists, the score is updated.
 *
 * A new sorted set is created at value if the key is an empty open key
 * setup for writing.
 *
 * Additional flags can be passed to the function via a pointer, the flags
 * are both used to receive input and to communicate state when the function
 * returns. 'flagsptr' can be NULL if no special flags are used.
 *
 * The input flags are:
 *
 * REDISMODULE_ZADD_XX: Element must already exist. Do nothing otherwise.
 * REDISMODULE_ZADD_NX: Element must not exist. Do nothing otherwise.
 *
 * The output flags are:
 *
 * REDISMODULE_ZADD_ADDED: The new element was added to the sorted set.
 * REDISMODULE_ZADD_UPDATED: The score of the element was updated.
 * REDISMODULE_ZADD_NOP: No operation was performed because XX or NX flags.
 *
 * On success the function returns REDISMODULE_OK. On the following errors
 * REDISMODULE_ERR is returned:
 *
 * * The key was not opened for writing.
 * * The key is of the wrong type.
 * * 'score' double value is not a number (NaN).
 */
int RM_ZsetAdd(RedisModuleKey *key, double score, RedisModuleString *ele, int *flagsptr) {
    int flags = 0;
    if (!(key->mode & REDISMODULE_WRITE)) return REDISMODULE_ERR;
    if (key->value && key->value->type != OBJ_ZSET) return REDISMODULE_ERR;
    if (key->value == NULL) moduleCreateEmptyKey(key,REDISMODULE_KEYTYPE_ZSET);
    if (flagsptr) flags = RM_ZsetAddFlagsToCoreFlags(*flagsptr);
    if (zsetAdd(key->value,score,ele->ptr,&flags,NULL) == 0) {
        if (flagsptr) *flagsptr = 0;
        return REDISMODULE_ERR;
    }
    if (flagsptr) *flagsptr = RM_ZsetAddFlagsFromCoreFlags(flags);
    return REDISMODULE_OK;
}

/* This function works exactly like RM_ZsetAdd(), but instead of setting
 * a new score, the score of the existing element is incremented, or if the
 * element does not already exist, it is added assuming the old score was
 * zero.
 *
 * The input and output flags, and the return value, have the same exact
 * meaning, with the only difference that this function will return
 * REDISMODULE_ERR even when 'score' is a valid double number, but adding it
 * to the existing score resuts into a NaN (not a number) condition.
 *
 * This function has an additional field 'newscore', if not NULL is filled
 * with the new score of the element after the increment, if no error
 * is returned. */
int RM_ZsetIncrby(RedisModuleKey *key, double score, RedisModuleString *ele, int *flagsptr, double *newscore) {
    int flags = 0;
    if (!(key->mode & REDISMODULE_WRITE)) return REDISMODULE_ERR;
    if (key->value && key->value->type != OBJ_ZSET) return REDISMODULE_ERR;
    if (key->value == NULL) moduleCreateEmptyKey(key,REDISMODULE_KEYTYPE_ZSET);
    if (flagsptr) flags = RM_ZsetAddFlagsToCoreFlags(*flagsptr);
    flags |= ZADD_INCR;
    if (zsetAdd(key->value,score,ele->ptr,&flags,newscore) == 0) {
        if (flagsptr) *flagsptr = 0;
        return REDISMODULE_ERR;
    }
    /* zsetAdd() may signal back that the resulting score is not a number. */
    if (flagsptr && (*flagsptr & ZADD_NAN)) {
        *flagsptr = 0;
        return REDISMODULE_ERR;
    }
    if (flagsptr) *flagsptr = RM_ZsetAddFlagsFromCoreFlags(flags);
    return REDISMODULE_OK;
}

/* Remove the specified element from the sorted set.
 * The function returns REDISMODULE_OK on success, and REDISMODULE_ERR
 * on one of the following conditions:
 *
 * * The key was not opened for writing.
 * * The key is of the wrong type.
 *
 * The return value does NOT indicate the fact the element was really
 * removed (since it existed) or not, just if the function was executed
 * with success.
 *
 * In order to know if the element was removed, the additional argument
 * 'deleted' must be passed, that populates the integer by reference
 * setting it to 1 or 0 depending on the outcome of the operation.
 * The 'deleted' argument can be NULL if the caller is not interested
 * to know if the element was really removed.
 *
 * Empty keys will be handled correctly by doing nothing. */
int RM_ZsetRem(RedisModuleKey *key, RedisModuleString *ele, int *deleted) {
    if (!(key->mode & REDISMODULE_WRITE)) return REDISMODULE_ERR;
    if (key->value && key->value->type != OBJ_ZSET) return REDISMODULE_ERR;
    if (key->value != NULL && zsetDel(key->value,ele->ptr)) {
        if (deleted) *deleted = 1;
    } else {
        if (deleted) *deleted = 0;
    }
    return REDISMODULE_OK;
}

/* On success retrieve the double score associated at the sorted set element
 * 'ele' and returns REDISMODULE_OK. Otherwise REDISMODULE_ERR is returned
 * to signal one of the following conditions:
 *
 * * There is no such element 'ele' in the sorted set.
 * * The key is not a sorted set.
 * * The key is an open empty key.
 */
int RM_ZsetScore(RedisModuleKey *key, RedisModuleString *ele, double *score) {
    if (key->value == NULL) return REDISMODULE_ERR;
    if (key->value->type != OBJ_ZSET) return REDISMODULE_ERR;
    if (zsetScore(key->value,ele->ptr,score) == C_ERR) return REDISMODULE_ERR;
    return REDISMODULE_OK;
}

/* --------------------------------------------------------------------------
 * Key API for Sorted Set iterator
 * -------------------------------------------------------------------------- */

void zsetKeyReset(RedisModuleKey *key) {
    key->ztype = REDISMODULE_ZSET_RANGE_NONE;
    key->zcurrent = NULL;
    key->zer = 1;
}

/* Stop a sorted set iteration. */
void RM_ZsetRangeStop(RedisModuleKey *key) {
    /* Free resources if needed. */
    if (key->ztype == REDISMODULE_ZSET_RANGE_LEX)
        zslFreeLexRange(&key->zlrs);
    /* Setup sensible values so that misused iteration API calls when an
     * iterator is not active will result into something more sensible
     * than crashing. */
    zsetKeyReset(key);
}

/* Return the "End of range" flag value to signal the end of the iteration. */
int RM_ZsetRangeEndReached(RedisModuleKey *key) {
    return key->zer;
}

/* Helper function for RM_ZsetFirstInScoreRange() and RM_ZsetLastInScoreRange().
 * Setup the sorted set iteration according to the specified score range
 * (see the functions calling it for more info). If 'first' is true the
 * first element in the range is used as a starting point for the iterator
 * otherwise the last. Return REDISMODULE_OK on success otherwise
 * REDISMODULE_ERR. */
int zsetInitScoreRange(RedisModuleKey *key, double min, double max, int minex, int maxex, int first) {
    if (!key->value || key->value->type != OBJ_ZSET) return REDISMODULE_ERR;

    RM_ZsetRangeStop(key);
    key->ztype = REDISMODULE_ZSET_RANGE_SCORE;
    key->zer = 0;

    /* Setup the range structure used by the sorted set core implementation
     * in order to seek at the specified element. */
    zrangespec *zrs = &key->zrs;
    zrs->min = min;
    zrs->max = max;
    zrs->minex = minex;
    zrs->maxex = maxex;

    if (key->value->encoding == OBJ_ENCODING_ZIPLIST) {
        key->zcurrent = first ? zzlFirstInRange(key->value->ptr,zrs) :
                                zzlLastInRange(key->value->ptr,zrs);
    } else if (key->value->encoding == OBJ_ENCODING_SKIPLIST) {
        zset *zs = key->value->ptr;
        zskiplist *zsl = zs->zsl;
        key->zcurrent = first ? zslFirstInRange(zsl,zrs) :
                                zslLastInRange(zsl,zrs);
    } else {
        serverPanic("Unsupported zset encoding");
    }
    if (key->zcurrent == NULL) key->zer = 1;
    return REDISMODULE_OK;
}

/* Setup a sorted set iterator seeking the first element in the specified
 * range. Returns REDISMODULE_OK if the iterator was correctly initialized
 * otherwise REDISMODULE_ERR is returned in the following conditions:
 *
 * 1. The value stored at key is not a sorted set or the key is empty.
 *
 * The range is specified according to the two double values 'min' and 'max'.
 * Both can be infinite using the following two macros:
 *
 * REDISMODULE_POSITIVE_INFINITE for positive infinite value
 * REDISMODULE_NEGATIVE_INFINITE for negative infinite value
 *
 * 'minex' and 'maxex' parameters, if true, respectively setup a range
 * where the min and max value are exclusive (not included) instead of
 * inclusive. */
int RM_ZsetFirstInScoreRange(RedisModuleKey *key, double min, double max, int minex, int maxex) {
    return zsetInitScoreRange(key,min,max,minex,maxex,1);
}

/* Exactly like RedisModule_ZsetFirstInScoreRange() but the last element of
 * the range is selected for the start of the iteration instead. */
int RM_ZsetLastInScoreRange(RedisModuleKey *key, double min, double max, int minex, int maxex) {
    return zsetInitScoreRange(key,min,max,minex,maxex,0);
}

/* Helper function for RM_ZsetFirstInLexRange() and RM_ZsetLastInLexRange().
 * Setup the sorted set iteration according to the specified lexicographical
 * range (see the functions calling it for more info). If 'first' is true the
 * first element in the range is used as a starting point for the iterator
 * otherwise the last. Return REDISMODULE_OK on success otherwise
 * REDISMODULE_ERR.
 *
 * Note that this function takes 'min' and 'max' in the same form of the
 * Redis ZRANGEBYLEX command. */
int zsetInitLexRange(RedisModuleKey *key, RedisModuleString *min, RedisModuleString *max, int first) {
    if (!key->value || key->value->type != OBJ_ZSET) return REDISMODULE_ERR;

    RM_ZsetRangeStop(key);
    key->zer = 0;

    /* Setup the range structure used by the sorted set core implementation
     * in order to seek at the specified element. */
    zlexrangespec *zlrs = &key->zlrs;
    if (zslParseLexRange(min, max, zlrs) == C_ERR) return REDISMODULE_ERR;

    /* Set the range type to lex only after successfully parsing the range,
     * otherwise we don't want the zlexrangespec to be freed. */
    key->ztype = REDISMODULE_ZSET_RANGE_LEX;

    if (key->value->encoding == OBJ_ENCODING_ZIPLIST) {
        key->zcurrent = first ? zzlFirstInLexRange(key->value->ptr,zlrs) :
                                zzlLastInLexRange(key->value->ptr,zlrs);
    } else if (key->value->encoding == OBJ_ENCODING_SKIPLIST) {
        zset *zs = key->value->ptr;
        zskiplist *zsl = zs->zsl;
        key->zcurrent = first ? zslFirstInLexRange(zsl,zlrs) :
                                zslLastInLexRange(zsl,zlrs);
    } else {
        serverPanic("Unsupported zset encoding");
    }
    if (key->zcurrent == NULL) key->zer = 1;

    return REDISMODULE_OK;
}

/* Setup a sorted set iterator seeking the first element in the specified
 * lexicographical range. Returns REDISMODULE_OK if the iterator was correctly
 * initialized otherwise REDISMODULE_ERR is returned in the
 * following conditions:
 *
 * 1. The value stored at key is not a sorted set or the key is empty.
 * 2. The lexicographical range 'min' and 'max' format is invalid.
 *
 * 'min' and 'max' should be provided as two RedisModuleString objects
 * in the same format as the parameters passed to the ZRANGEBYLEX command.
 * The function does not take ownership of the objects, so they can be released
 * ASAP after the iterator is setup. */
int RM_ZsetFirstInLexRange(RedisModuleKey *key, RedisModuleString *min, RedisModuleString *max) {
    return zsetInitLexRange(key,min,max,1);
}

/* Exactly like RedisModule_ZsetFirstInLexRange() but the last element of
 * the range is selected for the start of the iteration instead. */
int RM_ZsetLastInLexRange(RedisModuleKey *key, RedisModuleString *min, RedisModuleString *max) {
    return zsetInitLexRange(key,min,max,0);
}

/* Return the current sorted set element of an active sorted set iterator
 * or NULL if the range specified in the iterator does not include any
 * element. */
RedisModuleString *RM_ZsetRangeCurrentElement(RedisModuleKey *key, double *score) {
    RedisModuleString *str;

    if (key->zcurrent == NULL) return NULL;
    if (key->value->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *eptr, *sptr;
        eptr = key->zcurrent;
        sds ele = ziplistGetObject(eptr);
        if (score) {
            sptr = ziplistNext(key->value->ptr,eptr);
            *score = zzlGetScore(sptr);
        }
        str = createObject(OBJ_STRING,ele);
    } else if (key->value->encoding == OBJ_ENCODING_SKIPLIST) {
        zskiplistNode *ln = key->zcurrent;
        if (score) *score = ln->score;
        str = createStringObject(ln->ele,sdslen(ln->ele));
    } else {
        serverPanic("Unsupported zset encoding");
    }
    autoMemoryAdd(key->ctx,REDISMODULE_AM_STRING,str);
    return str;
}

/* Go to the next element of the sorted set iterator. Returns 1 if there was
 * a next element, 0 if we are already at the latest element or the range
 * does not include any item at all. */
int RM_ZsetRangeNext(RedisModuleKey *key) {
    if (!key->ztype || !key->zcurrent) return 0; /* No active iterator. */

    if (key->value->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *zl = key->value->ptr;
        unsigned char *eptr = key->zcurrent;
        unsigned char *next;
        next = ziplistNext(zl,eptr); /* Skip element. */
        if (next) next = ziplistNext(zl,next); /* Skip score. */
        if (next == NULL) {
            key->zer = 1;
            return 0;
        } else {
            /* Are we still within the range? */
            if (key->ztype == REDISMODULE_ZSET_RANGE_SCORE) {
                /* Fetch the next element score for the
                 * range check. */
                unsigned char *saved_next = next;
                next = ziplistNext(zl,next); /* Skip next element. */
                double score = zzlGetScore(next); /* Obtain the next score. */
                if (!zslValueLteMax(score,&key->zrs)) {
                    key->zer = 1;
                    return 0;
                }
                next = saved_next;
            } else if (key->ztype == REDISMODULE_ZSET_RANGE_LEX) {
                if (!zzlLexValueLteMax(next,&key->zlrs)) {
                    key->zer = 1;
                    return 0;
                }
            }
            key->zcurrent = next;
            return 1;
        }
    } else if (key->value->encoding == OBJ_ENCODING_SKIPLIST) {
        zskiplistNode *ln = key->zcurrent, *next = ln->level[0].forward;
        if (next == NULL) {
            key->zer = 1;
            return 0;
        } else {
            /* Are we still within the range? */
            if (key->ztype == REDISMODULE_ZSET_RANGE_SCORE &&
                !zslValueLteMax(ln->score,&key->zrs))
            {
                key->zer = 1;
                return 0;
            } else if (key->ztype == REDISMODULE_ZSET_RANGE_LEX) {
                if (!zslLexValueLteMax(ln->ele,&key->zlrs)) {
                    key->zer = 1;
                    return 0;
                }
            }
            key->zcurrent = next;
            return 1;
        }
    } else {
        serverPanic("Unsupported zset encoding");
    }
}

/* Go to the previous element of the sorted set iterator. Returns 1 if there was
 * a previous element, 0 if we are already at the first element or the range
 * does not include any item at all. */
int RM_ZsetRangePrev(RedisModuleKey *key) {
    if (!key->ztype || !key->zcurrent) return 0; /* No active iterator. */

    if (key->value->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *zl = key->value->ptr;
        unsigned char *eptr = key->zcurrent;
        unsigned char *prev;
        prev = ziplistPrev(zl,eptr); /* Go back to previous score. */
        if (prev) prev = ziplistPrev(zl,prev); /* Back to previous ele. */
        if (prev == NULL) {
            key->zer = 1;
            return 0;
        } else {
            /* Are we still within the range? */
            if (key->ztype == REDISMODULE_ZSET_RANGE_SCORE) {
                /* Fetch the previous element score for the
                 * range check. */
                unsigned char *saved_prev = prev;
                prev = ziplistNext(zl,prev); /* Skip element to get the score.*/
                double score = zzlGetScore(prev); /* Obtain the prev score. */
                if (!zslValueGteMin(score,&key->zrs)) {
                    key->zer = 1;
                    return 0;
                }
                prev = saved_prev;
            } else if (key->ztype == REDISMODULE_ZSET_RANGE_LEX) {
                if (!zzlLexValueGteMin(prev,&key->zlrs)) {
                    key->zer = 1;
                    return 0;
                }
            }
            key->zcurrent = prev;
            return 1;
        }
    } else if (key->value->encoding == OBJ_ENCODING_SKIPLIST) {
        zskiplistNode *ln = key->zcurrent, *prev = ln->backward;
        if (prev == NULL) {
            key->zer = 1;
            return 0;
        } else {
            /* Are we still within the range? */
            if (key->ztype == REDISMODULE_ZSET_RANGE_SCORE &&
                !zslValueGteMin(ln->score,&key->zrs))
            {
                key->zer = 1;
                return 0;
            } else if (key->ztype == REDISMODULE_ZSET_RANGE_LEX) {
                if (!zslLexValueGteMin(prev->ele,&key->zlrs)) {
                    key->zer = 1;
                    return 0;
                }
            }
            key->zcurrent = prev;
            return 1;
        }
    } else {
        serverPanic("Unsupported zset encoding");
    }
}

/* --------------------------------------------------------------------------
 * Key API for Hash type
 * -------------------------------------------------------------------------- */

/* Set the field of the specified hash field to the specified value.
 * If the key is an empty key open for writing, it is created with an empty
 * hash value, in order to set the specified field.
 *
 * The function is variadic and the user must specify pairs of field
 * names and values, both as RedisModuleString pointers (unless the
 * CFIELD option is set, see later).
 *
 * Example to set the hash argv[1] to the value argv[2]:
 *
 *  RedisModule_HashSet(key,REDISMODULE_HASH_NONE,argv[1],argv[2],NULL);
 *
 * The function can also be used in order to delete fields (if they exist)
 * by setting them to the specified value of REDISMODULE_HASH_DELETE:
 *
 *  RedisModule_HashSet(key,REDISMODULE_HASH_NONE,argv[1],
 *                      REDISMODULE_HASH_DELETE,NULL);
 *
 * The behavior of the command changes with the specified flags, that can be
 * set to REDISMODULE_HASH_NONE if no special behavior is needed.
 *
 * REDISMODULE_HASH_NX: The operation is performed only if the field was not
 *                     already existing in the hash.
 * REDISMODULE_HASH_XX: The operation is performed only if the field was
 *                     already existing, so that a new value could be
 *                     associated to an existing filed, but no new fields
 *                     are created.
 * REDISMODULE_HASH_CFIELDS: The field names passed are null terminated C
 *                          strings instead of RedisModuleString objects.
 *
 * Unless NX is specified, the command overwrites the old field value with
 * the new one.
 *
 * When using REDISMODULE_HASH_CFIELDS, field names are reported using
 * normal C strings, so for example to delete the field "foo" the following
 * code can be used:
 *
 *  RedisModule_HashSet(key,REDISMODULE_HASH_CFIELDS,"foo",
 *                      REDISMODULE_HASH_DELETE,NULL);
 *
 * Return value:
 *
 * The number of fields updated (that may be less than the number of fields
 * specified because of the XX or NX options).
 *
 * In the following case the return value is always zero:
 *
 * * The key was not open for writing.
 * * The key was associated with a non Hash value.
 */
int RM_HashSet(RedisModuleKey *key, int flags, ...) {
    va_list ap;
    if (!(key->mode & REDISMODULE_WRITE)) return 0;
    if (key->value && key->value->type != OBJ_HASH) return 0;
    if (key->value == NULL) moduleCreateEmptyKey(key,REDISMODULE_KEYTYPE_HASH);

    int updated = 0;
    va_start(ap, flags);
    while(1) {
        RedisModuleString *field, *value;
        /* Get the field and value objects. */
        if (flags & REDISMODULE_HASH_CFIELDS) {
            char *cfield = va_arg(ap,char*);
            if (cfield == NULL) break;
            field = createRawStringObject(cfield,strlen(cfield));
        } else {
            field = va_arg(ap,RedisModuleString*);
            if (field == NULL) break;
        }
        value = va_arg(ap,RedisModuleString*);

        /* Handle XX and NX */
        if (flags & (REDISMODULE_HASH_XX|REDISMODULE_HASH_NX)) {
            int exists = hashTypeExists(key->value, field->ptr);
            if (((flags & REDISMODULE_HASH_XX) && !exists) ||
                ((flags & REDISMODULE_HASH_NX) && exists))
            {
                if (flags & REDISMODULE_HASH_CFIELDS) decrRefCount(field);
                continue;
            }
        }

        /* Handle deletion if value is REDISMODULE_HASH_DELETE. */
        if (value == REDISMODULE_HASH_DELETE) {
            updated += hashTypeDelete(key->value, field->ptr);
            if (flags & REDISMODULE_HASH_CFIELDS) decrRefCount(field);
            continue;
        }

        int low_flags = HASH_SET_COPY;
        /* If CFIELDS is active, we can pass the ownership of the
         * SDS object to the low level function that sets the field
         * to avoid a useless copy. */
        if (flags & REDISMODULE_HASH_CFIELDS)
            low_flags |= HASH_SET_TAKE_FIELD;
        updated += hashTypeSet(key->value, field->ptr, value->ptr, low_flags);

        /* If CFIELDS is active, SDS string ownership is now of hashTypeSet(),
         * however we still have to release the 'field' object shell. */
        if (flags & REDISMODULE_HASH_CFIELDS) {
           field->ptr = NULL; /* Prevent the SDS string from being freed. */
           decrRefCount(field);
        }
    }
    va_end(ap);
    moduleDelKeyIfEmpty(key);
    return updated;
}

/* Get fields from an hash value. This function is called using a variable
 * number of arguments, alternating a field name (as a StringRedisModule
 * pointer) with a pointer to a StringRedisModule pointer, that is set to the
 * value of the field if the field exist, or NULL if the field did not exist.
 * At the end of the field/value-ptr pairs, NULL must be specified as last
 * argument to signal the end of the arguments in the variadic function.
 *
 * This is an example usage:
 *
 *      RedisModuleString *first, *second;
 *      RedisModule_HashGet(mykey,REDISMODULE_HASH_NONE,argv[1],&first,
 *                      argv[2],&second,NULL);
 *
 * As with RedisModule_HashSet() the behavior of the command can be specified
 * passing flags different than REDISMODULE_HASH_NONE:
 *
 * REDISMODULE_HASH_CFIELD: field names as null terminated C strings.
 *
 * REDISMODULE_HASH_EXISTS: instead of setting the value of the field
 * expecting a RedisModuleString pointer to pointer, the function just
 * reports if the field esists or not and expects an integer pointer
 * as the second element of each pair.
 *
 * Example of REDISMODULE_HASH_CFIELD:
 *
 *      RedisModuleString *username, *hashedpass;
 *      RedisModule_HashGet(mykey,"username",&username,"hp",&hashedpass, NULL);
 *
 * Example of REDISMODULE_HASH_EXISTS:
 *
 *      int exists;
 *      RedisModule_HashGet(mykey,argv[1],&exists,NULL);
 *
 * The function returns REDISMODULE_OK on success and REDISMODULE_ERR if
 * the key is not an hash value.
 *
 * Memory management:
 *
 * The returned RedisModuleString objects should be released with
 * RedisModule_FreeString(), or by enabling automatic memory management.
 */
int RM_HashGet(RedisModuleKey *key, int flags, ...) {
    va_list ap;
    if (key->value && key->value->type != OBJ_HASH) return REDISMODULE_ERR;

    va_start(ap, flags);
    while(1) {
        RedisModuleString *field, **valueptr;
        int *existsptr;
        /* Get the field object and the value pointer to pointer. */
        if (flags & REDISMODULE_HASH_CFIELDS) {
            char *cfield = va_arg(ap,char*);
            if (cfield == NULL) break;
            field = createRawStringObject(cfield,strlen(cfield));
        } else {
            field = va_arg(ap,RedisModuleString*);
            if (field == NULL) break;
        }

        /* Query the hash for existence or value object. */
        if (flags & REDISMODULE_HASH_EXISTS) {
            existsptr = va_arg(ap,int*);
            if (key->value)
                *existsptr = hashTypeExists(key->value,field->ptr);
            else
                *existsptr = 0;
        } else {
            valueptr = va_arg(ap,RedisModuleString**);
            if (key->value) {
                *valueptr = hashTypeGetValueObject(key->value,field->ptr);
                if (*valueptr) {
                    robj *decoded = getDecodedObject(*valueptr);
                    decrRefCount(*valueptr);
                    *valueptr = decoded;
                }
                if (*valueptr)
                    autoMemoryAdd(key->ctx,REDISMODULE_AM_STRING,*valueptr);
            } else {
                *valueptr = NULL;
            }
        }

        /* Cleanup */
        if (flags & REDISMODULE_HASH_CFIELDS) decrRefCount(field);
    }
    va_end(ap);
    return REDISMODULE_OK;
}

/* --------------------------------------------------------------------------
 * Redis <-> Modules generic Call() API
 * -------------------------------------------------------------------------- */

/* Create a new RedisModuleCallReply object. The processing of the reply
 * is lazy, the object is just populated with the raw protocol and later
 * is processed as needed. Initially we just make sure to set the right
 * reply type, which is extremely cheap to do. */
RedisModuleCallReply *moduleCreateCallReplyFromProto(RedisModuleCtx *ctx, sds proto) {
    RedisModuleCallReply *reply = zmalloc(sizeof(*reply));
    reply->ctx = ctx;
    reply->proto = proto;
    reply->protolen = sdslen(proto);
    reply->flags = REDISMODULE_REPLYFLAG_TOPARSE; /* Lazy parsing. */
    switch(proto[0]) {
    case '$':
    case '+': reply->type = REDISMODULE_REPLY_STRING; break;
    case '-': reply->type = REDISMODULE_REPLY_ERROR; break;
    case ':': reply->type = REDISMODULE_REPLY_INTEGER; break;
    case '*': reply->type = REDISMODULE_REPLY_ARRAY; break;
    default: reply->type = REDISMODULE_REPLY_UNKNOWN; break;
    }
    if ((proto[0] == '*' || proto[0] == '$') && proto[1] == '-')
        reply->type = REDISMODULE_REPLY_NULL;
    return reply;
}

void moduleParseCallReply_Int(RedisModuleCallReply *reply);
void moduleParseCallReply_BulkString(RedisModuleCallReply *reply);
void moduleParseCallReply_SimpleString(RedisModuleCallReply *reply);
void moduleParseCallReply_Array(RedisModuleCallReply *reply);

/* Do nothing if REDISMODULE_REPLYFLAG_TOPARSE is false, otherwise
 * use the protcol of the reply in reply->proto in order to fill the
 * reply with parsed data according to the reply type. */
void moduleParseCallReply(RedisModuleCallReply *reply) {
    if (!(reply->flags & REDISMODULE_REPLYFLAG_TOPARSE)) return;
    reply->flags &= ~REDISMODULE_REPLYFLAG_TOPARSE;

    switch(reply->proto[0]) {
    case ':': moduleParseCallReply_Int(reply); break;
    case '$': moduleParseCallReply_BulkString(reply); break;
    case '-': /* handled by next item. */
    case '+': moduleParseCallReply_SimpleString(reply); break;
    case '*': moduleParseCallReply_Array(reply); break;
    }
}

void moduleParseCallReply_Int(RedisModuleCallReply *reply) {
    char *proto = reply->proto;
    char *p = strchr(proto+1,'\r');

    string2ll(proto+1,p-proto-1,&reply->val.ll);
    reply->protolen = p-proto+2;
    reply->type = REDISMODULE_REPLY_INTEGER;
}

void moduleParseCallReply_BulkString(RedisModuleCallReply *reply) {
    char *proto = reply->proto;
    char *p = strchr(proto+1,'\r');
    long long bulklen;

    string2ll(proto+1,p-proto-1,&bulklen);
    if (bulklen == -1) {
        reply->protolen = p-proto+2;
        reply->type = REDISMODULE_REPLY_NULL;
    } else {
        reply->val.str = p+2;
        reply->len = bulklen;
        reply->protolen = p-proto+2+bulklen+2;
        reply->type = REDISMODULE_REPLY_STRING;
    }
}

void moduleParseCallReply_SimpleString(RedisModuleCallReply *reply) {
    char *proto = reply->proto;
    char *p = strchr(proto+1,'\r');

    reply->val.str = proto+1;
    reply->len = p-proto-1;
    reply->protolen = p-proto+2;
    reply->type = proto[0] == '+' ? REDISMODULE_REPLY_STRING :
                                    REDISMODULE_REPLY_ERROR;
}

void moduleParseCallReply_Array(RedisModuleCallReply *reply) {
    char *proto = reply->proto;
    char *p = strchr(proto+1,'\r');
    long long arraylen, j;

    string2ll(proto+1,p-proto-1,&arraylen);
    p += 2;

    if (arraylen == -1) {
        reply->protolen = p-proto;
        reply->type = REDISMODULE_REPLY_NULL;
        return;
    }

    reply->val.array = zmalloc(sizeof(RedisModuleCallReply)*arraylen);
    reply->len = arraylen;
    for (j = 0; j < arraylen; j++) {
        RedisModuleCallReply *ele = reply->val.array+j;
        ele->flags = REDISMODULE_REPLYFLAG_NESTED |
                     REDISMODULE_REPLYFLAG_TOPARSE;
        ele->proto = p;
        ele->ctx = reply->ctx;
        moduleParseCallReply(ele);
        p += ele->protolen;
    }
    reply->protolen = p-proto;
    reply->type = REDISMODULE_REPLY_ARRAY;
}

/* Free a Call reply and all the nested replies it contains if it's an
 * array. */
void RM_FreeCallReply_Rec(RedisModuleCallReply *reply, int freenested){
    /* Don't free nested replies by default: the user must always free the
     * toplevel reply. However be gentle and don't crash if the module
     * misuses the API. */
    if (!freenested && reply->flags & REDISMODULE_REPLYFLAG_NESTED) return;

    if (!(reply->flags & REDISMODULE_REPLYFLAG_TOPARSE)) {
        if (reply->type == REDISMODULE_REPLY_ARRAY) {
            size_t j;
            for (j = 0; j < reply->len; j++)
                RM_FreeCallReply_Rec(reply->val.array+j,1);
            zfree(reply->val.array);
        }
    }

    /* For nested replies, we don't free reply->proto (which if not NULL
     * references the parent reply->proto buffer), nor the structure
     * itself which is allocated as an array of structures, and is freed
     * when the array value is released. */
    if (!(reply->flags & REDISMODULE_REPLYFLAG_NESTED)) {
        if (reply->proto) sdsfree(reply->proto);
        zfree(reply);
    }
}

/* Wrapper for the recursive free reply function. This is needed in order
 * to have the first level function to return on nested replies, but only
 * if called by the module API. */
void RM_FreeCallReply(RedisModuleCallReply *reply) {
    RM_FreeCallReply_Rec(reply,0);
    autoMemoryFreed(reply->ctx,REDISMODULE_AM_REPLY,reply);
}

/* Return the reply type. */
int RM_CallReplyType(RedisModuleCallReply *reply) {
    if (!reply) return REDISMODULE_REPLY_UNKNOWN;
    return reply->type;
}

/* Return the reply type length, where applicable. */
size_t RM_CallReplyLength(RedisModuleCallReply *reply) {
    moduleParseCallReply(reply);
    switch(reply->type) {
    case REDISMODULE_REPLY_STRING:
    case REDISMODULE_REPLY_ERROR:
    case REDISMODULE_REPLY_ARRAY:
        return reply->len;
    default:
        return 0;
    }
}

/* Return the 'idx'-th nested call reply element of an array reply, or NULL
 * if the reply type is wrong or the index is out of range. */
RedisModuleCallReply *RM_CallReplyArrayElement(RedisModuleCallReply *reply, size_t idx) {
    moduleParseCallReply(reply);
    if (reply->type != REDISMODULE_REPLY_ARRAY) return NULL;
    if (idx >= reply->len) return NULL;
    return reply->val.array+idx;
}

/* Return the long long of an integer reply. */
long long RM_CallReplyInteger(RedisModuleCallReply *reply) {
    moduleParseCallReply(reply);
    if (reply->type != REDISMODULE_REPLY_INTEGER) return LLONG_MIN;
    return reply->val.ll;
}

/* Return the pointer and length of a string or error reply. */
const char *RM_CallReplyStringPtr(RedisModuleCallReply *reply, size_t *len) {
    moduleParseCallReply(reply);
    if (reply->type != REDISMODULE_REPLY_STRING &&
        reply->type != REDISMODULE_REPLY_ERROR) return NULL;
    if (len) *len = reply->len;
    return reply->val.str;
}

/* Return a new string object from a call reply of type string, error or
 * integer. Otherwise (wrong reply type) return NULL. */
RedisModuleString *RM_CreateStringFromCallReply(RedisModuleCallReply *reply) {
    moduleParseCallReply(reply);
    switch(reply->type) {
    case REDISMODULE_REPLY_STRING:
    case REDISMODULE_REPLY_ERROR:
        return RM_CreateString(reply->ctx,reply->val.str,reply->len);
    case REDISMODULE_REPLY_INTEGER: {
        char buf[64];
        int len = ll2string(buf,sizeof(buf),reply->val.ll);
        return RM_CreateString(reply->ctx,buf,len);
        }
    default: return NULL;
    }
}

/* Returns an array of robj pointers, and populates *argc with the number
 * of items, by parsing the format specifier "fmt" as described for
 * the RM_Call(), RM_Replicate() and other module APIs.
 *
 * The integer pointed by 'flags' is populated with flags according
 * to special modifiers in "fmt". For now only one exists:
 *
 * "!" -> REDISMODULE_ARGV_REPLICATE
 *
 * On error (format specifier error) NULL is returned and nothing is
 * allocated. On success the argument vector is returned. */

#define REDISMODULE_ARGV_REPLICATE (1<<0)

robj **moduleCreateArgvFromUserFormat(const char *cmdname, const char *fmt, int *argcp, int *flags, va_list ap) {
    int argc = 0, argv_size, j;
    robj **argv = NULL;

    /* As a first guess to avoid useless reallocations, size argv to
     * hold one argument for each char specifier in 'fmt'. */
    argv_size = strlen(fmt)+1; /* +1 because of the command name. */
    argv = zrealloc(argv,sizeof(robj*)*argv_size);

    /* Build the arguments vector based on the format specifier. */
    argv[0] = createStringObject(cmdname,strlen(cmdname));
    argc++;

    /* Create the client and dispatch the command. */
    const char *p = fmt;
    while(*p) {
        if (*p == 'c') {
            char *cstr = va_arg(ap,char*);
            argv[argc++] = createStringObject(cstr,strlen(cstr));
        } else if (*p == 's') {
            robj *obj = va_arg(ap,void*);
            argv[argc++] = obj;
            incrRefCount(obj);
        } else if (*p == 'b') {
            char *buf = va_arg(ap,char*);
            size_t len = va_arg(ap,size_t);
            argv[argc++] = createStringObject(buf,len);
        } else if (*p == 'l') {
            long ll = va_arg(ap,long long);
            argv[argc++] = createStringObjectFromLongLong(ll);
        } else if (*p == 'v') {
             /* A vector of strings */
             robj **v = va_arg(ap, void*);
             size_t vlen = va_arg(ap, size_t);

             /* We need to grow argv to hold the vector's elements.
              * We resize by vector_len-1 elements, because we held
              * one element in argv for the vector already */
             argv_size += vlen-1;
             argv = zrealloc(argv,sizeof(robj*)*argv_size);

             size_t i = 0;
             for (i = 0; i < vlen; i++) {
                 incrRefCount(v[i]);
                 argv[argc++] = v[i];
             }
        } else if (*p == '!') {
            if (flags) (*flags) |= REDISMODULE_ARGV_REPLICATE;
        } else {
            goto fmterr;
        }
        p++;
    }
    *argcp = argc;
    return argv;

fmterr:
    for (j = 0; j < argc; j++)
        decrRefCount(argv[j]);
    zfree(argv);
    return NULL;
}

/* Exported API to call any Redis command from modules.
 * On success a RedisModuleCallReply object is returned, otherwise
 * NULL is returned and errno is set to the following values:
 *
 * EINVAL: command non existing, wrong arity, wrong format specifier.
 * EPERM:  operation in Cluster instance with key in non local slot. */
RedisModuleCallReply *RM_Call(RedisModuleCtx *ctx, const char *cmdname, const char *fmt, ...) {
    struct redisCommand *cmd;
    client *c = NULL;
    robj **argv = NULL;
    int argc = 0, flags = 0;
    va_list ap;
    RedisModuleCallReply *reply = NULL;
    int replicate = 0; /* Replicate this command? */

    cmd = lookupCommandByCString((char*)cmdname);
    if (!cmd) {
        errno = EINVAL;
        return NULL;
    }

    /* Create the client and dispatch the command. */
    va_start(ap, fmt);
    c = createClient(-1);
    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,&flags,ap);
    replicate = flags & REDISMODULE_ARGV_REPLICATE;
    va_end(ap);

    /* Setup our fake client for command execution. */
    c->flags |= CLIENT_MODULE;
    c->argv = argv;
    c->argc = argc;
    c->cmd = c->lastcmd = cmd;
    /* We handle the above format error only when the client is setup so that
     * we can free it normally. */
    if (argv == NULL) goto cleanup;

    /* Basic arity checks. */
    if ((cmd->arity > 0 && cmd->arity != argc) || (argc < -cmd->arity)) {
        errno = EINVAL;
        goto cleanup;
    }

    /* If this is a Redis Cluster node, we need to make sure the module is not
     * trying to access non-local keys, with the exception of commands
     * received from our master. */
    if (server.cluster_enabled && !(ctx->client->flags & CLIENT_MASTER)) {
        /* Duplicate relevant flags in the module client. */
        c->flags &= ~(CLIENT_READONLY|CLIENT_ASKING);
        c->flags |= ctx->client->flags & (CLIENT_READONLY|CLIENT_ASKING);
        if (getNodeByQuery(c,c->cmd,c->argv,c->argc,NULL,NULL) !=
                           server.cluster->myself)
        {
            errno = EPERM;
            goto cleanup;
        }
    }

    /* If we are using single commands replication, we need to wrap what
     * we propagate into a MULTI/EXEC block, so that it will be atomic like
     * a Lua script in the context of AOF and slaves. */
    if (replicate) moduleReplicateMultiIfNeeded(ctx);

    /* Run the command */
    int call_flags = CMD_CALL_SLOWLOG | CMD_CALL_STATS;
    if (replicate) {
        call_flags |= CMD_CALL_PROPAGATE_AOF;
        call_flags |= CMD_CALL_PROPAGATE_REPL;
    }
    call(c,call_flags);

    /* Convert the result of the Redis command into a suitable Lua type.
     * The first thing we need is to create a single string from the client
     * output buffers. */
    sds proto = sdsnewlen(c->buf,c->bufpos);
    c->bufpos = 0;
    while(listLength(c->reply)) {
        sds o = listNodeValue(listFirst(c->reply));

        proto = sdscatsds(proto,o);
        listDelNode(c->reply,listFirst(c->reply));
    }
    reply = moduleCreateCallReplyFromProto(ctx,proto);
    autoMemoryAdd(ctx,REDISMODULE_AM_REPLY,reply);

cleanup:
    freeClient(c);
    return reply;
}

/* Return a pointer, and a length, to the protocol returned by the command
 * that returned the reply object. */
const char *RM_CallReplyProto(RedisModuleCallReply *reply, size_t *len) {
    if (reply->proto) *len = sdslen(reply->proto);
    return reply->proto;
}

/* --------------------------------------------------------------------------
 * Modules data types
 *
 * When String DMA or using existing data structures is not enough, it is
 * possible to create new data types from scratch and export them to
 * Redis. The module must provide a set of callbacks for handling the
 * new values exported (for example in order to provide RDB saving/loading,
 * AOF rewrite, and so forth). In this section we define this API.
 * -------------------------------------------------------------------------- */

/* Turn a 9 chars name in the specified charset and a 10 bit encver into
 * a single 64 bit unsigned integer that represents this exact module name
 * and version. This final number is called a "type ID" and is used when
 * writing module exported values to RDB files, in order to re-associate the
 * value to the right module to load them during RDB loading.
 *
 * If the string is not of the right length or the charset is wrong, or
 * if encver is outside the unsigned 10 bit integer range, 0 is returned,
 * otherwise the function returns the right type ID.
 *
 * The resulting 64 bit integer is composed as follows:
 *
 * (high order bits) 6|6|6|6|6|6|6|6|6|10 (low order bits)
 *
 * The first 6 bits value is the first character, name[0], while the last
 * 6 bits value, immediately before the 10 bits integer, is name[8].
 * The last 10 bits are the encoding version.
 *
 * Note that a name and encver combo of "AAAAAAAAA" and 0, will produce
 * zero as return value, that is the same we use to signal errors, thus
 * this combination is invalid, and also useless since type names should
 * try to be vary to avoid collisions. */

const char *ModuleTypeNameCharSet =
             "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
             "abcdefghijklmnopqrstuvwxyz"
             "0123456789-_";

uint64_t moduleTypeEncodeId(const char *name, int encver) {
    /* We use 64 symbols so that we can map each character into 6 bits
     * of the final output. */
    const char *cset = ModuleTypeNameCharSet;
    if (strlen(name) != 9) return 0;
    if (encver < 0 || encver > 1023) return 0;

    uint64_t id = 0;
    for (int j = 0; j < 9; j++) {
        char *p = strchr(cset,name[j]);
        if (!p) return 0;
        unsigned long pos = p-cset;
        id = (id << 6) | pos;
    }
    id = (id << 10) | encver;
    return id;
}

/* Search, in the list of exported data types of all the modules registered,
 * a type with the same name as the one given. Returns the moduleType
 * structure pointer if such a module is found, or NULL otherwise. */
moduleType *moduleTypeLookupModuleByName(const char *name) {
    dictIterator *di = dictGetIterator(modules);
    dictEntry *de;

    while ((de = dictNext(di)) != NULL) {
        struct RedisModule *module = dictGetVal(de);
        listIter li;
        listNode *ln;

        listRewind(module->types,&li);
        while((ln = listNext(&li))) {
            moduleType *mt = ln->value;
            if (memcmp(name,mt->name,sizeof(mt->name)) == 0) {
                dictReleaseIterator(di);
                return mt;
            }
        }
    }
    dictReleaseIterator(di);
    return NULL;
}

/* Lookup a module by ID, with caching. This function is used during RDB
 * loading. Modules exporting data types should never be able to unload, so
 * our cache does not need to expire. */
#define MODULE_LOOKUP_CACHE_SIZE 3

moduleType *moduleTypeLookupModuleByID(uint64_t id) {
    static struct {
        uint64_t id;
        moduleType *mt;
    } cache[MODULE_LOOKUP_CACHE_SIZE];

    /* Search in cache to start. */
    int j;
    for (j = 0; j < MODULE_LOOKUP_CACHE_SIZE; j++)
        if (cache[j].id == id) return cache[j].mt;

    /* Slow module by module lookup. */
    moduleType *mt = NULL;
    dictIterator *di = dictGetIterator(modules);
    dictEntry *de;

    while ((de = dictNext(di)) != NULL) {
        struct RedisModule *module = dictGetVal(de);
        listIter li;
        listNode *ln;

        listRewind(module->types,&li);
        while((ln = listNext(&li))) {
            mt = ln->value;
            /* Compare only the 54 bit module identifier and not the
             * encoding version. */
            if (mt->id >> 10 == id >> 10) break;
        }
    }
    dictReleaseIterator(di);

    /* Add to cache if possible. */
    if (mt && j < MODULE_LOOKUP_CACHE_SIZE) {
        cache[j].id = id;
        cache[j].mt = mt;
    }
    return mt;
}

/* Turn an (unresolved) module ID into a type name, to show the user an
 * error when RDB files contain module data we can't load. */
void moduleTypeNameByID(char *name, uint64_t moduleid) {
    const char *cset = ModuleTypeNameCharSet;

    name[0] = '\0';
    char *p = name+8;
    moduleid >>= 10;
    for (int j = 0; j < 9; j++) {
        *p-- = cset[moduleid & 63];
        moduleid >>= 6;
    }
}

/* Register a new data type exported by the module. The parameters are the
 * following. Please for in depth documentation check the modules API
 * documentation, especially the INTRO.md file.
 *
 * * **name**: A 9 characters data type name that MUST be unique in the Redis
 *   Modules ecosystem. Be creative... and there will be no collisions. Use
 *   the charset A-Z a-z 9-0, plus the two "-_" characters. A good
 *   idea is to use, for example `<typename>-<vendor>`. For example
 *   "tree-AntZ" may mean "Tree data structure by @antirez". To use both
 *   lower case and upper case letters helps in order to prevent collisions.
 * * **encver**: Encoding version, which is, the version of the serialization
 *   that a module used in order to persist data. As long as the "name"
 *   matches, the RDB loading will be dispatched to the type callbacks
 *   whatever 'encver' is used, however the module can understand if
 *   the encoding it must load are of an older version of the module.
 *   For example the module "tree-AntZ" initially used encver=0. Later
 *   after an upgrade, it started to serialize data in a different format
 *   and to register the type with encver=1. However this module may
 *   still load old data produced by an older version if the rdb_load
 *   callback is able to check the encver value and act accordingly.
 *   The encver must be a positive value between 0 and 1023.
 * * **rdb_load**: A callback function pointer that loads data from RDB files.
 * * **rdb_save**: A callback function pointer that saves data to RDB files.
 * * **aof_rewrite**: A callback function pointer that rewrites data as commands.
 * * **digest**: A callback function pointer that is used for `DEBUG DIGEST`.
 * * **free**: A callback function pointer that can free a type value.
 *
 * Note: the module name "AAAAAAAAA" is reserved and produces an error, it
 * happens to be pretty lame as well.
 *
 * If there is already a module registering a type with the same name,
 * and if the module name or encver is invalid, NULL is returned.
 * Otherwise the new type is registered into Redis, and a reference of
 * type RedisModuleType is returned: the caller of the function should store
 * this reference into a gobal variable to make future use of it in the
 * modules type API, since a single module may register multiple types.
 * Example code fragment:
 *
 *      static RedisModuleType *BalancedTreeType;
 *
 *      int RedisModule_OnLoad(RedisModuleCtx *ctx) {
 *          // some code here ...
 *          BalancedTreeType = RM_CreateDataType(...);
 *      }
 */
moduleType *RM_CreateDataType(RedisModuleCtx *ctx, const char *name, int encver, moduleTypeLoadFunc rdb_load, moduleTypeSaveFunc rdb_save, moduleTypeRewriteFunc aof_rewrite, moduleTypeDigestFunc digest, moduleTypeFreeFunc free) {
    uint64_t id = moduleTypeEncodeId(name,encver);
    if (id == 0) return NULL;
    if (moduleTypeLookupModuleByName(name) != NULL) return NULL;

    moduleType *mt = zmalloc(sizeof(*mt));
    mt->id = id;
    mt->module = ctx->module;
    mt->rdb_load = rdb_load;
    mt->rdb_save = rdb_save;
    mt->aof_rewrite = aof_rewrite;
    mt->digest = digest;
    mt->free = free;
    memcpy(mt->name,name,sizeof(mt->name));
    listAddNodeTail(ctx->module->types,mt);
    return mt;
}

/* If the key is open for writing, set the specified module type object
 * as the value of the key, deleting the old value if any.
 * On success REDISMODULE_OK is returned. If the key is not open for
 * writing or there is an active iterator, REDISMODULE_ERR is returned. */
int RM_ModuleTypeSetValue(RedisModuleKey *key, moduleType *mt, void *value) {
    if (!(key->mode & REDISMODULE_WRITE) || key->iter) return REDISMODULE_ERR;
    RM_DeleteKey(key);
    robj *o = createModuleObject(mt,value);
    setKey(key->db,key->key,o);
    decrRefCount(o);
    key->value = o;
    return REDISMODULE_OK;
}

/* Assuming RedisModule_KeyType() returned REDISMODULE_KEYTYPE_MODULE on
 * the key, returns the moduel type pointer of the value stored at key.
 *
 * If the key is NULL, is not associated with a module type, or is empty,
 * then NULL is returned instead. */
moduleType *RM_ModuleTypeGetType(RedisModuleKey *key) {
    if (key == NULL ||
        key->value == NULL ||
        RM_KeyType(key) != REDISMODULE_KEYTYPE_MODULE) return NULL;
    moduleValue *mv = key->value->ptr;
    return mv->type;
}

/* Assuming RedisModule_KeyType() returned REDISMODULE_KEYTYPE_MODULE on
 * the key, returns the module type low-level value stored at key, as
 * it was set by the user via RedisModule_ModuleTypeSet().
 *
 * If the key is NULL, is not associated with a module type, or is empty,
 * then NULL is returned instead. */
void *RM_ModuleTypeGetValue(RedisModuleKey *key) {
    if (key == NULL ||
        key->value == NULL ||
        RM_KeyType(key) != REDISMODULE_KEYTYPE_MODULE) return NULL;
    moduleValue *mv = key->value->ptr;
    return mv->value;
}

/* --------------------------------------------------------------------------
 * RDB loading and saving functions
 * -------------------------------------------------------------------------- */

/* Called when there is a load error in the context of a module. This cannot
 * be recovered like for the built-in types. */
void moduleRDBLoadError(RedisModuleIO *io) {
    serverLog(LL_WARNING,
        "Error loading data from RDB (short read or EOF). "
        "Read performed by module '%s' about type '%s' "
        "after reading '%llu' bytes of a value.",
        io->type->module->name,
        io->type->name,
        (unsigned long long)io->bytes);
    exit(1);
}

/* Save an unsigned 64 bit value into the RDB file. This function should only
 * be called in the context of the rdb_save method of modules implementing new
 * data types. */
void RM_SaveUnsigned(RedisModuleIO *io, uint64_t value) {
    if (io->error) return;
    int retval = rdbSaveLen(io->rio, value);
    if (retval == -1) {
        io->error = 1;
    } else {
        io->bytes += retval;
    }
}

/* Load an unsigned 64 bit value from the RDB file. This function should only
 * be called in the context of the rdb_load method of modules implementing
 * new data types. */
uint64_t RM_LoadUnsigned(RedisModuleIO *io) {
    uint64_t value;
    int retval = rdbLoadLenByRef(io->rio, NULL, &value);
    if (retval == -1) {
        moduleRDBLoadError(io);
        return 0; /* Never reached. */
    }
    return value;
}

/* Like RedisModule_SaveUnsigned() but for signed 64 bit values. */
void RM_SaveSigned(RedisModuleIO *io, int64_t value) {
    union {uint64_t u; int64_t i;} conv;
    conv.i = value;
    RM_SaveUnsigned(io,conv.u);
}

/* Like RedisModule_LoadUnsigned() but for signed 64 bit values. */
int64_t RM_LoadSigned(RedisModuleIO *io) {
    union {uint64_t u; int64_t i;} conv;
    conv.u = RM_LoadUnsigned(io);
    return conv.i;
}

/* In the context of the rdb_save method of a module type, saves a
 * string into the RDB file taking as input a RedisModuleString.
 *
 * The string can be later loaded with RedisModule_LoadString() or
 * other Load family functions expecting a serialized string inside
 * the RDB file. */
void RM_SaveString(RedisModuleIO *io, RedisModuleString *s) {
    if (io->error) return;
    int retval = rdbSaveStringObject(io->rio,s);
    if (retval == -1) {
        io->error = 1;
    } else {
        io->bytes += retval;
    }
}

/* Like RedisModule_SaveString() but takes a raw C pointer and length
 * as input. */
void RM_SaveStringBuffer(RedisModuleIO *io, const char *str, size_t len) {
    if (io->error) return;
    int retval = rdbSaveRawString(io->rio,(unsigned char*)str,len);
    if (retval == -1) {
        io->error = 1;
    } else {
        io->bytes += retval;
    }
}

/* Implements RM_LoadString() and RM_LoadStringBuffer() */
void *moduleLoadString(RedisModuleIO *io, int plain, size_t *lenptr) {
    void *s = rdbGenericLoadStringObject(io->rio,
              plain ? RDB_LOAD_PLAIN : RDB_LOAD_NONE, lenptr);
    if (s == NULL) {
        moduleRDBLoadError(io);
        return NULL; /* Never reached. */
    }
    return s;
}

/* In the context of the rdb_load method of a module data type, loads a string
 * from the RDB file, that was previously saved with RedisModule_SaveString()
 * functions family.
 *
 * The returned string is a newly allocated RedisModuleString object, and
 * the user should at some point free it with a call to RedisModule_FreeString().
 *
 * If the data structure does not store strings as RedisModuleString objects,
 * the similar function RedisModule_LoadStringBuffer() could be used instead. */
RedisModuleString *RM_LoadString(RedisModuleIO *io) {
    return moduleLoadString(io,0,NULL);
}

/* Like RedisModule_LoadString() but returns an heap allocated string that
 * was allocated with RedisModule_Alloc(), and can be resized or freed with
 * RedisModule_Realloc() or RedisModule_Free().
 *
 * The size of the string is stored at '*lenptr' if not NULL.
 * The returned string is not automatically NULL termianted, it is loaded
 * exactly as it was stored inisde the RDB file. */
char *RM_LoadStringBuffer(RedisModuleIO *io, size_t *lenptr) {
    return moduleLoadString(io,1,lenptr);
}

/* In the context of the rdb_save method of a module data type, saves a double
 * value to the RDB file. The double can be a valid number, a NaN or infinity.
 * It is possible to load back the value with RedisModule_LoadDouble(). */
void RM_SaveDouble(RedisModuleIO *io, double value) {
    if (io->error) return;
    int retval = rdbSaveBinaryDoubleValue(io->rio, value);
    if (retval == -1) {
        io->error = 1;
    } else {
        io->bytes += retval;
    }
}

/* In the context of the rdb_save method of a module data type, loads back the
 * double value saved by RedisModule_SaveDouble(). */
double RM_LoadDouble(RedisModuleIO *io) {
    double value;
    int retval = rdbLoadBinaryDoubleValue(io->rio, &value);
    if (retval == -1) {
        moduleRDBLoadError(io);
        return 0; /* Never reached. */
    }
    return value;
}

/* In the context of the rdb_save method of a module data type, saves a float 
 * value to the RDB file. The float can be a valid number, a NaN or infinity.
 * It is possible to load back the value with RedisModule_LoadFloat(). */
void RM_SaveFloat(RedisModuleIO *io, float value) {
    if (io->error) return;
    int retval = rdbSaveBinaryFloatValue(io->rio, value);
    if (retval == -1) {
        io->error = 1;
    } else {
        io->bytes += retval;
    }
}

/* In the context of the rdb_save method of a module data type, loads back the
 * float value saved by RedisModule_SaveFloat(). */
float RM_LoadFloat(RedisModuleIO *io) {
    float value;
    int retval = rdbLoadBinaryFloatValue(io->rio, &value);
    if (retval == -1) {
        moduleRDBLoadError(io);
        return 0; /* Never reached. */
    }
    return value;
}

/* --------------------------------------------------------------------------
 * AOF API for modules data types
 * -------------------------------------------------------------------------- */

/* Emits a command into the AOF during the AOF rewriting process. This function
 * is only called in the context of the aof_rewrite method of data types exported
 * by a module. The command works exactly like RedisModule_Call() in the way
 * the parameters are passed, but it does not return anything as the error
 * handling is performed by Redis itself. */
void RM_EmitAOF(RedisModuleIO *io, const char *cmdname, const char *fmt, ...) {
    if (io->error) return;
    struct redisCommand *cmd;
    robj **argv = NULL;
    int argc = 0, flags = 0, j;
    va_list ap;

    cmd = lookupCommandByCString((char*)cmdname);
    if (!cmd) {
        serverLog(LL_WARNING,
            "Fatal: AOF method for module data type '%s' tried to "
            "emit unknown command '%s'",
            io->type->name, cmdname);
        io->error = 1;
        errno = EINVAL;
        return;
    }

    /* Emit the arguments into the AOF in Redis protocol format. */
    va_start(ap, fmt);
    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,&flags,ap);
    va_end(ap);
    if (argv == NULL) {
        serverLog(LL_WARNING,
            "Fatal: AOF method for module data type '%s' tried to "
            "call RedisModule_EmitAOF() with wrong format specifiers '%s'",
            io->type->name, fmt);
        io->error = 1;
        errno = EINVAL;
        return;
    }

    /* Bulk count. */
    if (!io->error && rioWriteBulkCount(io->rio,'*',argc) == 0)
        io->error = 1;

    /* Arguments. */
    for (j = 0; j < argc; j++) {
        if (!io->error && rioWriteBulkObject(io->rio,argv[j]) == 0)
            io->error = 1;
        decrRefCount(argv[j]);
    }
    zfree(argv);
    return;
}

/* --------------------------------------------------------------------------
 * IO context handling
 * -------------------------------------------------------------------------- */

RedisModuleCtx *RM_GetContextFromIO(RedisModuleIO *io) {
    if (io->ctx) return io->ctx; /* Can't have more than one... */
    RedisModuleCtx ctxtemplate = REDISMODULE_CTX_INIT;
    io->ctx = zmalloc(sizeof(RedisModuleCtx));
    *(io->ctx) = ctxtemplate;
    io->ctx->module = io->type->module;
    io->ctx->client = NULL;
    return io->ctx;
}

/* --------------------------------------------------------------------------
 * Logging
 * -------------------------------------------------------------------------- */

/* This is the low level function implementing both:
 *
 *  RM_Log()
 *  RM_LogIOError()
 *
 */
void RM_LogRaw(RedisModule *module, const char *levelstr, const char *fmt, va_list ap) {
    char msg[LOG_MAX_LEN];
    size_t name_len;
    int level;

    if (!strcasecmp(levelstr,"debug")) level = LL_DEBUG;
    else if (!strcasecmp(levelstr,"verbose")) level = LL_VERBOSE;
    else if (!strcasecmp(levelstr,"notice")) level = LL_NOTICE;
    else if (!strcasecmp(levelstr,"warning")) level = LL_WARNING;
    else level = LL_VERBOSE; /* Default. */

    name_len = snprintf(msg, sizeof(msg),"<%s> ", module->name);
    vsnprintf(msg + name_len, sizeof(msg) - name_len, fmt, ap);
    serverLogRaw(level,msg);
}

/*
 * Produces a log message to the standard Redis log, the format accepts
 * printf-alike specifiers, while level is a string describing the log
 * level to use when emitting the log, and must be one of the following:
 *
 * * "debug"
 * * "verbose"
 * * "notice"
 * * "warning"
 *
 * If the specified log level is invalid, verbose is used by default.
 * There is a fixed limit to the length of the log line this function is able
 * to emit, this limti is not specified but is guaranteed to be more than
 * a few lines of text.
 */
void RM_Log(RedisModuleCtx *ctx, const char *levelstr, const char *fmt, ...) {
    if (!ctx->module) return;   /* Can only log if module is initialized */

    va_list ap;
    va_start(ap, fmt);
    RM_LogRaw(ctx->module,levelstr,fmt,ap);
    va_end(ap);
}

/* Log errors from RDB / AOF serialization callbacks.
 *
 * This function should be used when a callback is returning a critical
 * error to the caller since cannot load or save the data for some
 * critical reason. */
void RM_LogIOError(RedisModuleIO *io, const char *levelstr, const char *fmt, ...) {
    va_list ap;
    va_start(ap, fmt);
    RM_LogRaw(io->type->module,levelstr,fmt,ap);
    va_end(ap);
}

/* --------------------------------------------------------------------------
 * Blocking clients from modules
 * -------------------------------------------------------------------------- */

/* This is called from blocked.c in order to unblock a client: may be called
 * for multiple reasons while the client is in the middle of being blocked
 * because the client is terminated, but is also called for cleanup when a
 * client is unblocked in a clean way after replaying.
 *
 * What we do here is just to set the client to NULL in the redis module
 * blocked client handle. This way if the client is terminated while there
 * is a pending threaded operation involving the blocked client, we'll know
 * that the client no longer exists and no reply callback should be called.
 *
 * The structure RedisModuleBlockedClient will be always deallocated when
 * running the list of clients blocked by a module that need to be unblocked. */
void unblockClientFromModule(client *c) {
    RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
    bc->client = NULL;
}

/* Block a client in the context of a blocking command, returning an handle
 * which will be used, later, in order to block the client with a call to
 * RedisModule_UnblockClient(). The arguments specify callback functions
 * and a timeout after which the client is unblocked.
 *
 * The callbacks are called in the following contexts:
 *
 * reply_callback:  called after a successful RedisModule_UnblockClient() call
 *                  in order to reply to the client and unblock it.
 * reply_timeout:   called when the timeout is reached in order to send an
 *                  error to the client.
 * free_privdata:   called in order to free the privata data that is passed
 *                  by RedisModule_UnblockClient() call.
 */
RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(void*), long long timeout_ms) {
    client *c = ctx->client;
    c->bpop.module_blocked_handle = zmalloc(sizeof(RedisModuleBlockedClient));
    RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;

    bc->client = c;
    bc->module = ctx->module;
    bc->reply_callback = reply_callback;
    bc->timeout_callback = timeout_callback;
    bc->free_privdata = free_privdata;
    bc->privdata = NULL;
    c->bpop.timeout = timeout_ms ? (mstime()+timeout_ms) : 0;

    blockClient(c,BLOCKED_MODULE);
    return bc;
}

/* Unblock a client blocked by `RedisModule_BlockedClient`. This will trigger
 * the reply callbacks to be called in order to reply to the client.
 * The 'privdata' argument will be accessible by the reply callback, so
 * the caller of this function can pass any value that is needed in order to
 * actually reply to the client.
 *
 * A common usage for 'privdata' is a thread that computes something that
 * needs to be passed to the client, included but not limited some slow
 * to compute reply or some reply obtained via networking.
 *
 * Note: this function can be called from threads spawned by the module. */
int RM_UnblockClient(RedisModuleBlockedClient *bc, void *privdata) {
    pthread_mutex_lock(&moduleUnblockedClientsMutex);
    bc->privdata = privdata;
    listAddNodeTail(moduleUnblockedClients,bc);
    pthread_mutex_unlock(&moduleUnblockedClientsMutex);
    return REDISMODULE_OK;
}

/* Abort a blocked client blocking operation: the client will be unblocked
 * without firing the reply callback. */
int RM_AbortBlock(RedisModuleBlockedClient *bc) {
    bc->reply_callback = NULL;
    return RM_UnblockClient(bc,NULL);
}

/* This function will check the moduleUnblockedClients queue in order to
 * call the reply callback and really unblock the client.
 *
 * Clients end into this list because of calls to RM_UnblockClient(),
 * however it is possible that while the module was doing work for the
 * blocked client, it was terminated by Redis (for timeout or other reasons).
 * When this happens the RedisModuleBlockedClient structure in the queue
 * will have the 'client' field set to NULL. */
void moduleHandleBlockedClients(void) {
    listNode *ln;
    RedisModuleBlockedClient *bc;

    pthread_mutex_lock(&moduleUnblockedClientsMutex);
    while (listLength(moduleUnblockedClients)) {
        ln = listFirst(moduleUnblockedClients);
        bc = ln->value;
        client *c = bc->client;
        listDelNode(moduleUnblockedClients,ln);
        pthread_mutex_unlock(&moduleUnblockedClientsMutex);

        /* Release the lock during the loop, as long as we don't
         * touch the shared list. */

        if (c != NULL && bc->reply_callback != NULL) {
            RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
            ctx.flags |= REDISMODULE_CTX_BLOCKED_REPLY;
            ctx.blocked_privdata = bc->privdata;
            ctx.module = bc->module;
            ctx.client = bc->client;
            bc->reply_callback(&ctx,(void**)c->argv,c->argc);
            moduleHandlePropagationAfterCommandCallback(&ctx);
            moduleFreeContext(&ctx);
        }
        if (bc->privdata && bc->free_privdata)
            bc->free_privdata(bc->privdata);
        zfree(bc);
        if (c != NULL) unblockClient(bc->client);

        /* Lock again before to iterate the loop. */
        pthread_mutex_lock(&moduleUnblockedClientsMutex);
    }
    pthread_mutex_unlock(&moduleUnblockedClientsMutex);
}

/* Called when our client timed out. After this function unblockClient()
 * is called, and it will invalidate the blocked client. So this function
 * does not need to do any cleanup. Eventually the module will call the
 * API to unblock the client and the memory will be released. */
void moduleBlockedClientTimedOut(client *c) {
    RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
    RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
    ctx.flags |= REDISMODULE_CTX_BLOCKED_TIMEOUT;
    ctx.module = bc->module;
    ctx.client = bc->client;
    bc->timeout_callback(&ctx,(void**)c->argv,c->argc);
    moduleFreeContext(&ctx);
}

/* Return non-zero if a module command was called in order to fill the
 * reply for a blocked client. */
int RM_IsBlockedReplyRequest(RedisModuleCtx *ctx) {
    return (ctx->flags & REDISMODULE_CTX_BLOCKED_REPLY) != 0;
}

/* Return non-zero if a module command was called in order to fill the
 * reply for a blocked client that timed out. */
int RM_IsBlockedTimeoutRequest(RedisModuleCtx *ctx) {
    return (ctx->flags & REDISMODULE_CTX_BLOCKED_TIMEOUT) != 0;
}

/* Get the privata data set by RedisModule_UnblockClient() */
void *RM_GetBlockedClientPrivateData(RedisModuleCtx *ctx) {
    return ctx->blocked_privdata;
}

/* --------------------------------------------------------------------------
 * Modules API internals
 * -------------------------------------------------------------------------- */

/* server.moduleapi dictionary type. Only uses plain C strings since
 * this gets queries from modules. */

unsigned int dictCStringKeyHash(const void *key) {
    return dictGenHashFunction((unsigned char*)key, strlen((char*)key));
}

int dictCStringKeyCompare(void *privdata, const void *key1, const void *key2) {
    DICT_NOTUSED(privdata);
    return strcmp(key1,key2) == 0;
}

dictType moduleAPIDictType = {
    dictCStringKeyHash,        /* hash function */
    NULL,                      /* key dup */
    NULL,                      /* val dup */
    dictCStringKeyCompare,     /* key compare */
    NULL,                      /* key destructor */
    NULL                       /* val destructor */
};

int moduleRegisterApi(const char *funcname, void *funcptr) {
    return dictAdd(server.moduleapi, (char*)funcname, funcptr);
}

#define REGISTER_API(name) \
    moduleRegisterApi("RedisModule_" #name, (void *)(unsigned long)RM_ ## name)

/* Global initialization at Redis startup. */
void moduleRegisterCoreAPI(void);

void moduleInitModulesSystem(void) {
    moduleUnblockedClients = listCreate();

    server.loadmodule_queue = listCreate();
    modules = dictCreate(&modulesDictType,NULL);
    moduleRegisterCoreAPI();
}

/* Load all the modules in the server.loadmodule_queue list, which is
 * populated by `loadmodule` directives in the configuration file.
 * We can't load modules directly when processing the configuration file
 * because the server must be fully initialized before loading modules.
 *
 * The function aborts the server on errors, since to start with missing
 * modules is not considered sane: clients may rely on the existance of
 * given commands, loading AOF also may need some modules to exist, and
 * if this instance is a slave, it must understand commands from master. */
void moduleLoadFromQueue(void) {
    listIter li;
    listNode *ln;

    listRewind(server.loadmodule_queue,&li);
    while((ln = listNext(&li))) {
        struct moduleLoadQueueEntry *loadmod = ln->value;
        if (moduleLoad(loadmod->path,(void **)loadmod->argv,loadmod->argc)
            == C_ERR)
        {
            serverLog(LL_WARNING,
                "Can't load module from %s: server aborting",
                loadmod->path);
            exit(1);
        }
    }
}

void moduleFreeModuleStructure(struct RedisModule *module) {
    listRelease(module->types);
    sdsfree(module->name);
    zfree(module);
}

/* Load a module and initialize it. On success C_OK is returned, otherwise
 * C_ERR is returned. */
int moduleLoad(const char *path, void **module_argv, int module_argc) {
    int (*onload)(void *, void **, int);
    void *handle;
    RedisModuleCtx ctx = REDISMODULE_CTX_INIT;

    handle = dlopen(path,RTLD_NOW|RTLD_LOCAL);
    if (handle == NULL) {
        serverLog(LL_WARNING, "Module %s failed to load: %s", path, dlerror());
        return C_ERR;
    }
    onload = (int (*)(void *, void **, int))(unsigned long) dlsym(handle,"RedisModule_OnLoad");
    if (onload == NULL) {
        serverLog(LL_WARNING,
            "Module %s does not export RedisModule_OnLoad() "
            "symbol. Module not loaded.",path);
        return C_ERR;
    }
    if (onload((void*)&ctx,module_argv,module_argc) == REDISMODULE_ERR) {
        if (ctx.module) moduleFreeModuleStructure(ctx.module);
        dlclose(handle);
        serverLog(LL_WARNING,
            "Module %s initialization failed. Module not loaded",path);
        return C_ERR;
    }

    /* Redis module loaded! Register it. */
    dictAdd(modules,ctx.module->name,ctx.module);
    ctx.module->handle = handle;
    serverLog(LL_NOTICE,"Module '%s' loaded from %s",ctx.module->name,path);
    moduleFreeContext(&ctx);
    return C_OK;
}

/* Unload the module registered with the specified name. On success
 * C_OK is returned, otherwise C_ERR is returned and errno is set
 * to the following values depending on the type of error:
 *
 * ENONET: No such module having the specified name.
 * EBUSY: The module exports a new data type and can only be reloaded. */
int moduleUnload(sds name) {
    struct RedisModule *module = dictFetchValue(modules,name);

    if (module == NULL) {
        errno = ENOENT;
        return REDISMODULE_ERR;
    }

    if (listLength(module->types)) {
        errno = EBUSY;
        return REDISMODULE_ERR;
    }

    /* Unregister all the commands registered by this module. */
    dictIterator *di = dictGetSafeIterator(server.commands);
    dictEntry *de;
    while ((de = dictNext(di)) != NULL) {
        struct redisCommand *cmd = dictGetVal(de);
        if (cmd->proc == RedisModuleCommandDispatcher) {
            RedisModuleCommandProxy *cp =
                (void*)(unsigned long)cmd->getkeys_proc;
            sds cmdname = cp->rediscmd->name;
            if (cp->module == module) {
                dictDelete(server.commands,cmdname);
                dictDelete(server.orig_commands,cmdname);
                sdsfree(cmdname);
                zfree(cp->rediscmd);
                zfree(cp);
            }
        }
    }
    dictReleaseIterator(di);

    /* Unregister all the hooks. TODO: Yet no hooks support here. */

    /* Unload the dynamic library. */
    if (dlclose(module->handle) == -1) {
        char *error = dlerror();
        if (error == NULL) error = "Unknown error";
        serverLog(LL_WARNING,"Error when trying to close the %s module: %s",
            module->name, error);
    }

    /* Remove from list of modules. */
    serverLog(LL_NOTICE,"Module %s unloaded",module->name);
    dictDelete(modules,module->name);
    module->name = NULL; /* The name was already freed by dictDelete(). */
    moduleFreeModuleStructure(module);

    return REDISMODULE_OK;
}

/* Redis MODULE command.
 *
 * MODULE LOAD <path> [args...] */
void moduleCommand(client *c) {
    char *subcmd = c->argv[1]->ptr;

    if (!strcasecmp(subcmd,"load") && c->argc >= 3) {
        robj **argv = NULL;
        int argc = 0;

        if (c->argc > 3) {
            argc = c->argc - 3;
            argv = &c->argv[3];
        }

        if (moduleLoad(c->argv[2]->ptr,(void **)argv,argc) == C_OK)
            addReply(c,shared.ok);
        else
            addReplyError(c,
                "Error loading the extension. Please check the server logs.");
    } else if (!strcasecmp(subcmd,"unload") && c->argc == 3) {
        if (moduleUnload(c->argv[2]->ptr) == C_OK)
            addReply(c,shared.ok);
        else {
            char *errmsg;
            switch(errno) {
            case ENOENT:
                errmsg = "no such module with that name";
                break;
            case EBUSY:
                errmsg = "the module exports one or more module-side data types, can't unload";
                break;
            default:
                errmsg = "operation not possible.";
                break;
            }
            addReplyErrorFormat(c,"Error unloading module: %s",errmsg);
        }
    } else if (!strcasecmp(subcmd,"list") && c->argc == 2) {
        dictIterator *di = dictGetIterator(modules);
        dictEntry *de;

        addReplyMultiBulkLen(c,dictSize(modules));
        while ((de = dictNext(di)) != NULL) {
            sds name = dictGetKey(de);
            struct RedisModule *module = dictGetVal(de);
            addReplyMultiBulkLen(c,4);
            addReplyBulkCString(c,"name");
            addReplyBulkCBuffer(c,name,sdslen(name));
            addReplyBulkCString(c,"ver");
            addReplyLongLong(c,module->ver);
        }
        dictReleaseIterator(di);
    } else {
        addReply(c,shared.syntaxerr);
    }
}

/* Register all the APIs we export. Keep this function at the end of the
 * file so that's easy to seek it to add new entries. */
void moduleRegisterCoreAPI(void) {
    server.moduleapi = dictCreate(&moduleAPIDictType,NULL);
    REGISTER_API(Alloc);
    REGISTER_API(Calloc);
    REGISTER_API(Realloc);
    REGISTER_API(Free);
    REGISTER_API(Strdup);
    REGISTER_API(CreateCommand);
    REGISTER_API(SetModuleAttribs);
    REGISTER_API(WrongArity);
    REGISTER_API(ReplyWithLongLong);
    REGISTER_API(ReplyWithError);
    REGISTER_API(ReplyWithSimpleString);
    REGISTER_API(ReplyWithArray);
    REGISTER_API(ReplySetArrayLength);
    REGISTER_API(ReplyWithString);
    REGISTER_API(ReplyWithStringBuffer);
    REGISTER_API(ReplyWithNull);
    REGISTER_API(ReplyWithCallReply);
    REGISTER_API(ReplyWithDouble);
    REGISTER_API(GetSelectedDb);
    REGISTER_API(SelectDb);
    REGISTER_API(OpenKey);
    REGISTER_API(CloseKey);
    REGISTER_API(KeyType);
    REGISTER_API(ValueLength);
    REGISTER_API(ListPush);
    REGISTER_API(ListPop);
    REGISTER_API(StringToLongLong);
    REGISTER_API(StringToDouble);
    REGISTER_API(Call);
    REGISTER_API(CallReplyProto);
    REGISTER_API(FreeCallReply);
    REGISTER_API(CallReplyInteger);
    REGISTER_API(CallReplyType);
    REGISTER_API(CallReplyLength);
    REGISTER_API(CallReplyArrayElement);
    REGISTER_API(CallReplyStringPtr);
    REGISTER_API(CreateStringFromCallReply);
    REGISTER_API(CreateString);
    REGISTER_API(CreateStringFromLongLong);
    REGISTER_API(CreateStringFromString);
    REGISTER_API(CreateStringPrintf);
    REGISTER_API(FreeString);
    REGISTER_API(StringPtrLen);
    REGISTER_API(AutoMemory);
    REGISTER_API(Replicate);
    REGISTER_API(ReplicateVerbatim);
    REGISTER_API(DeleteKey);
    REGISTER_API(StringSet);
    REGISTER_API(StringDMA);
    REGISTER_API(StringTruncate);
    REGISTER_API(SetExpire);
    REGISTER_API(GetExpire);
    REGISTER_API(ZsetAdd);
    REGISTER_API(ZsetIncrby);
    REGISTER_API(ZsetScore);
    REGISTER_API(ZsetRem);
    REGISTER_API(ZsetRangeStop);
    REGISTER_API(ZsetFirstInScoreRange);
    REGISTER_API(ZsetLastInScoreRange);
    REGISTER_API(ZsetFirstInLexRange);
    REGISTER_API(ZsetLastInLexRange);
    REGISTER_API(ZsetRangeCurrentElement);
    REGISTER_API(ZsetRangeNext);
    REGISTER_API(ZsetRangePrev);
    REGISTER_API(ZsetRangeEndReached);
    REGISTER_API(HashSet);
    REGISTER_API(HashGet);
    REGISTER_API(IsKeysPositionRequest);
    REGISTER_API(KeyAtPos);
    REGISTER_API(GetClientId);
    REGISTER_API(PoolAlloc);
    REGISTER_API(CreateDataType);
    REGISTER_API(ModuleTypeSetValue);
    REGISTER_API(ModuleTypeGetType);
    REGISTER_API(ModuleTypeGetValue);
    REGISTER_API(SaveUnsigned);
    REGISTER_API(LoadUnsigned);
    REGISTER_API(SaveSigned);
    REGISTER_API(LoadSigned);
    REGISTER_API(SaveString);
    REGISTER_API(SaveStringBuffer);
    REGISTER_API(LoadString);
    REGISTER_API(LoadStringBuffer);
    REGISTER_API(SaveDouble);
    REGISTER_API(LoadDouble);
    REGISTER_API(SaveFloat);
    REGISTER_API(LoadFloat);
    REGISTER_API(EmitAOF);
    REGISTER_API(Log);
    REGISTER_API(LogIOError);
    REGISTER_API(StringAppendBuffer);
    REGISTER_API(RetainString);
    REGISTER_API(StringCompare);
    REGISTER_API(GetContextFromIO);
    REGISTER_API(BlockClient);
    REGISTER_API(UnblockClient);
    REGISTER_API(IsBlockedReplyRequest);
    REGISTER_API(IsBlockedTimeoutRequest);
    REGISTER_API(GetBlockedClientPrivateData);
    REGISTER_API(AbortBlock);
    REGISTER_API(Milliseconds);
}